What is SQL used for?

SQL is used to store, query, and manage data in relational databases like MySQL, PostgreSQL, and SQL Server.

What is the difference between WHERE and HAVING?

WHERE filters rows before grouping, while HAVING filters groups after aggregation.

SQL Tutorial (Beginner to Advanced)

∙ Chapter 001

SQL Tutorial

Learn SQL Tutorial with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-tutorial.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT 'Hello SQL' AS message;`	Selects columns/expressions.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 002

SQL HOME

Learn SQL HOME with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-home.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT 'Hello SQL' AS message;`	Selects columns/expressions.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 003

SQL Intro

Learn SQL Intro with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-intro.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT 'Hello SQL' AS message;`	Selects columns/expressions.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 004

SQL Syntax

Learn SQL Syntax with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-syntax.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT customer_name, city`	Selects columns/expressions.
`FROM customers`	Chooses the source table(s).
`WHERE country = 'India'`	Filters rows before grouping.
`ORDER BY customer_name ASC;`	Sorts the result set.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 005

SQL Select

Learn SQL Select with a small query you can edit and run.

📝Syntax

SELECT columns
FROM table
WHERE condition
ORDER BY column DESC
LIMIT 10;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-select.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT customer_name, country`	Selects columns/expressions.
`FROM customers;`	Chooses the source table(s).

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 006

SQL Select Distinct

Learn SQL Select Distinct with a small query you can edit and run.

📝Syntax

SELECT columns
FROM table
WHERE condition
ORDER BY column DESC
LIMIT 10;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-select-distinct.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT DISTINCT country`	Selects columns/expressions.
`FROM customers;`	Chooses the source table(s).

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 007

SQL Where

Learn SQL Where with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-where.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT id, total_amount`	Selects columns/expressions.
`FROM orders`	Chooses the source table(s).
`WHERE total_amount > 500`	Filters rows before grouping.
`ORDER BY total_amount DESC;`	Sorts the result set.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 008

SQL Order By

Learn SQL Order By with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-order-by.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT customer_name, city`	Selects columns/expressions.
`FROM customers`	Chooses the source table(s).
`ORDER BY city ASC, customer_name ASC;`	Sorts the result set.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 009

SQL And

Learn SQL And with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-and.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT customer_name`	Selects columns/expressions.
`FROM customers`	Chooses the source table(s).
`WHERE country = 'India' AND city = 'Mumbai';`	Filters rows before grouping.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 010

SQL Or

Learn SQL Or with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-or.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT customer_name`	Selects columns/expressions.
`FROM customers`	Chooses the source table(s).
`WHERE country = 'USA' OR country = 'UK';`	Filters rows before grouping.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 011

SQL Not

Learn SQL Not with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-not.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT customer_name, country`	Selects columns/expressions.
`FROM customers`	Chooses the source table(s).
`WHERE NOT country = 'India';`	Filters rows before grouping.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 012

SQL Insert Into

Learn SQL Insert Into with a small query you can edit and run.

📝Syntax

INSERT INTO table (col1, col2)
VALUES (val1, val2);

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-insert-into.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`INSERT INTO customers (customer_name, city, country)`	Inserts new row(s).
`VALUES ('Zara', 'Dubai', 'UAE');`	SQL statement line.
`SELECT customer_name, country`	Selects columns/expressions.
`FROM customers`	Chooses the source table(s).
`ORDER BY id DESC`	Sorts the result set.
`LIMIT 3;`	Limits how many rows are returned.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 013

SQL Null Values

Learn SQL Null Values with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-null-values.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT customer_name, city`	Selects columns/expressions.
`FROM customers`	Chooses the source table(s).
`WHERE city IS NULL;`	Filters rows before grouping.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 014

SQL Update

Learn SQL Update with a small query you can edit and run.

📝Syntax

UPDATE table
SET col = value
WHERE condition;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-update.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`UPDATE customers`	Updates existing row(s).
`SET city = 'Pune'`	SQL statement line.
`WHERE customer_name = 'Aarav';`	Filters rows before grouping.
`SELECT customer_name, city`	Selects columns/expressions.
`FROM customers`	Chooses the source table(s).
`WHERE customer_name = 'Aarav';`	Filters rows before grouping.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 015

SQL Delete

Learn SQL Delete with a small query you can edit and run.

📝Syntax

DELETE FROM table
WHERE condition;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-delete.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`INSERT INTO customers (customer_name, city, country)`	Inserts new row(s).
`VALUES ('Temp', 'Nowhere', 'NA');`	SQL statement line.
`DELETE FROM customers WHERE customer_name = 'Temp';`	Deletes row(s).
`SELECT COUNT(*) AS customers`	Selects columns/expressions.
`FROM customers;`	Chooses the source table(s).

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 016

SQL Select Top

Learn SQL Select Top with a small query you can edit and run.

📝Syntax

SELECT columns
FROM table
WHERE condition
ORDER BY column DESC
LIMIT 10;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-select-top.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT id, total_amount`	Selects columns/expressions.
`FROM orders`	Chooses the source table(s).
`ORDER BY total_amount DESC`	Sorts the result set.
`LIMIT 2;`	Limits how many rows are returned.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 017

SQL Aggregate Functions

Learn SQL Aggregate Functions with a small query you can edit and run.

📝Syntax

SELECT col, COUNT(*)
FROM table
GROUP BY col
HAVING COUNT(*) > 1;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-aggregate-functions.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT`	SQL statement line.
`COUNT(*) AS order_count,`	SQL statement line.
`MIN(total_amount) AS min_total,`	SQL statement line.
`MAX(total_amount) AS max_total,`	SQL statement line.
`SUM(total_amount) AS sum_total,`	SQL statement line.
`AVG(total_amount) AS avg_total`	SQL statement line.
`FROM orders;`	Chooses the source table(s).

🏢Real-world

1Counts, totals, and averages for KPIs.
2Finding top customers/products by revenue.

⚠Common Mistakes

1Mixing non-aggregated columns without GROUP BY.
2Using WHERE instead of HAVING for aggregate filters.

✅Best Practices

1Group first, then filter aggregates with HAVING.
2Name aggregates with aliases (AS total_sales).

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 018

SQL Min()

Learn SQL Min() with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-min.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT`	SQL statement line.
`COUNT(*) AS order_count,`	SQL statement line.
`MIN(total_amount) AS min_total,`	SQL statement line.
`MAX(total_amount) AS max_total,`	SQL statement line.
`SUM(total_amount) AS sum_total,`	SQL statement line.
`AVG(total_amount) AS avg_total`	SQL statement line.
`FROM orders;`	Chooses the source table(s).

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 019

SQL Max()

Learn SQL Max() with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-max.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT`	SQL statement line.
`COUNT(*) AS order_count,`	SQL statement line.
`MIN(total_amount) AS min_total,`	SQL statement line.
`MAX(total_amount) AS max_total,`	SQL statement line.
`SUM(total_amount) AS sum_total,`	SQL statement line.
`AVG(total_amount) AS avg_total`	SQL statement line.
`FROM orders;`	Chooses the source table(s).

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 020

SQL Count()

Learn SQL Count() with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-count.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT`	SQL statement line.
`COUNT(*) AS order_count,`	SQL statement line.
`MIN(total_amount) AS min_total,`	SQL statement line.
`MAX(total_amount) AS max_total,`	SQL statement line.
`SUM(total_amount) AS sum_total,`	SQL statement line.
`AVG(total_amount) AS avg_total`	SQL statement line.
`FROM orders;`	Chooses the source table(s).

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 021

SQL Sum()

Learn SQL Sum() with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-sum.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT`	SQL statement line.
`COUNT(*) AS order_count,`	SQL statement line.
`MIN(total_amount) AS min_total,`	SQL statement line.
`MAX(total_amount) AS max_total,`	SQL statement line.
`SUM(total_amount) AS sum_total,`	SQL statement line.
`AVG(total_amount) AS avg_total`	SQL statement line.
`FROM orders;`	Chooses the source table(s).

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 022

SQL Avg()

Learn SQL Avg() with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-avg.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT`	SQL statement line.
`COUNT(*) AS order_count,`	SQL statement line.
`MIN(total_amount) AS min_total,`	SQL statement line.
`MAX(total_amount) AS max_total,`	SQL statement line.
`SUM(total_amount) AS sum_total,`	SQL statement line.
`AVG(total_amount) AS avg_total`	SQL statement line.
`FROM orders;`	Chooses the source table(s).

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 023

SQL Like

Learn SQL Like with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-like.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT customer_name`	Selects columns/expressions.
`FROM customers`	Chooses the source table(s).
`WHERE customer_name LIKE 'M%';`	Filters rows before grouping.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 024

SQL Wildcards

Learn SQL Wildcards with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-wildcards.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT customer_name`	Selects columns/expressions.
`FROM customers`	Chooses the source table(s).
`WHERE customer_name LIKE '_ia';`	Filters rows before grouping.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 025

SQL In

Learn SQL In with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-in.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT customer_name, country`	Selects columns/expressions.
`FROM customers`	Chooses the source table(s).
`WHERE country IN ('India', 'USA');`	Filters rows before grouping.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 026

SQL Between

Learn SQL Between with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-between.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT id, total_amount`	Selects columns/expressions.
`FROM orders`	Chooses the source table(s).
`WHERE total_amount BETWEEN 100 AND 1000`	Filters rows before grouping.
`ORDER BY total_amount DESC;`	Sorts the result set.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 027

SQL Aliases

Learn SQL Aliases with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-aliases.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT customer_name AS name, country AS c`	Selects columns/expressions.
`FROM customers`	Chooses the source table(s).
`ORDER BY name;`	Sorts the result set.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 028

SQL Joins

Learn SQL Joins with a small query you can edit and run.

📝Syntax

SELECT a.col, b.col
FROM a
JOIN b ON b.a_id = a.id;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-joins.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT o.id AS order_id, c.customer_name, o.total_amount`	Selects columns/expressions.
`FROM orders o`	Chooses the source table(s).
`JOIN customers c ON c.id = o.customer_id`	Combines rows from related tables.
`ORDER BY o.total_amount DESC;`	Sorts the result set.

🏢Real-world

1Combine customer + order data for reports.
2Enrich rows by joining lookup tables (products, departments).

⚠Common Mistakes

1Joining on the wrong key and duplicating rows.
2Using SELECT * with joins and getting ambiguous columns.

✅Best Practices

1Always join on the correct primary/foreign key.
2Alias tables (`c`, `o`) and select only needed columns.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 029

SQL Inner Join

Learn SQL Inner Join with a small query you can edit and run.

📝Syntax

SELECT a.col, b.col
FROM a
JOIN b ON b.a_id = a.id;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-inner-join.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT o.id AS order_id, c.customer_name, o.total_amount`	Selects columns/expressions.
`FROM orders o`	Chooses the source table(s).
`JOIN customers c ON c.id = o.customer_id`	Combines rows from related tables.
`ORDER BY o.total_amount DESC;`	Sorts the result set.

🏢Real-world

1Combine customer + order data for reports.
2Enrich rows by joining lookup tables (products, departments).

⚠Common Mistakes

1Joining on the wrong key and duplicating rows.
2Using SELECT * with joins and getting ambiguous columns.

✅Best Practices

1Always join on the correct primary/foreign key.
2Alias tables (`c`, `o`) and select only needed columns.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 030

SQL Left Join

Learn SQL Left Join with a small query you can edit and run.

📝Syntax

SELECT a.col, b.col
FROM a
JOIN b ON b.a_id = a.id;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-left-join.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT o.id AS order_id, c.customer_name, o.total_amount`	Selects columns/expressions.
`FROM orders o`	Chooses the source table(s).
`JOIN customers c ON c.id = o.customer_id`	Combines rows from related tables.
`ORDER BY o.total_amount DESC;`	Sorts the result set.

🏢Real-world

1Combine customer + order data for reports.
2Enrich rows by joining lookup tables (products, departments).

⚠Common Mistakes

1Joining on the wrong key and duplicating rows.
2Using SELECT * with joins and getting ambiguous columns.

✅Best Practices

1Always join on the correct primary/foreign key.
2Alias tables (`c`, `o`) and select only needed columns.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 031

SQL Right Join

Learn SQL Right Join with a small query you can edit and run.

📝Syntax

SELECT a.col, b.col
FROM a
JOIN b ON b.a_id = a.id;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-right-join.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT o.id AS order_id, c.customer_name, o.total_amount`	Selects columns/expressions.
`FROM orders o`	Chooses the source table(s).
`JOIN customers c ON c.id = o.customer_id`	Combines rows from related tables.
`ORDER BY o.total_amount DESC;`	Sorts the result set.

🏢Real-world

1Combine customer + order data for reports.
2Enrich rows by joining lookup tables (products, departments).

⚠Common Mistakes

1Joining on the wrong key and duplicating rows.
2Using SELECT * with joins and getting ambiguous columns.

✅Best Practices

1Always join on the correct primary/foreign key.
2Alias tables (`c`, `o`) and select only needed columns.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 032

SQL Full Join

Learn SQL Full Join with a small query you can edit and run.

📝Syntax

SELECT a.col, b.col
FROM a
JOIN b ON b.a_id = a.id;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-full-join.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT o.id AS order_id, c.customer_name, o.total_amount`	Selects columns/expressions.
`FROM orders o`	Chooses the source table(s).
`JOIN customers c ON c.id = o.customer_id`	Combines rows from related tables.
`ORDER BY o.total_amount DESC;`	Sorts the result set.

🏢Real-world

1Combine customer + order data for reports.
2Enrich rows by joining lookup tables (products, departments).

⚠Common Mistakes

1Joining on the wrong key and duplicating rows.
2Using SELECT * with joins and getting ambiguous columns.

✅Best Practices

1Always join on the correct primary/foreign key.
2Alias tables (`c`, `o`) and select only needed columns.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 033

SQL Self Join

Learn SQL Self Join with a small query you can edit and run.

📝Syntax

SELECT a.col, b.col
FROM a
JOIN b ON b.a_id = a.id;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-self-join.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT o.id AS order_id, c.customer_name, o.total_amount`	Selects columns/expressions.
`FROM orders o`	Chooses the source table(s).
`JOIN customers c ON c.id = o.customer_id`	Combines rows from related tables.
`ORDER BY o.total_amount DESC;`	Sorts the result set.

🏢Real-world

1Combine customer + order data for reports.
2Enrich rows by joining lookup tables (products, departments).

⚠Common Mistakes

1Joining on the wrong key and duplicating rows.
2Using SELECT * with joins and getting ambiguous columns.

✅Best Practices

1Always join on the correct primary/foreign key.
2Alias tables (`c`, `o`) and select only needed columns.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 034

SQL Union

Learn SQL Union with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-union.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT country AS label FROM customers`	Selects columns/expressions.
`UNION`	SQL statement line.
`SELECT department AS label FROM employees;`	Selects columns/expressions.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 035

SQL Union All

Learn SQL Union All with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-union-all.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT country AS label FROM customers`	Selects columns/expressions.
`UNION`	SQL statement line.
`SELECT department AS label FROM employees;`	Selects columns/expressions.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 036

SQL Group By

Learn SQL Group By with a small query you can edit and run.

📝Syntax

SELECT col, COUNT(*)
FROM table
GROUP BY col
HAVING COUNT(*) > 1;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-group-by.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT country, COUNT(*) AS customers`	Selects columns/expressions.
`FROM customers`	Chooses the source table(s).
`GROUP BY country`	Groups rows for aggregation.
`ORDER BY customers DESC;`	Sorts the result set.

🏢Real-world

1Counts, totals, and averages for KPIs.
2Finding top customers/products by revenue.

⚠Common Mistakes

1Mixing non-aggregated columns without GROUP BY.
2Using WHERE instead of HAVING for aggregate filters.

✅Best Practices

1Group first, then filter aggregates with HAVING.
2Name aggregates with aliases (AS total_sales).

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 037

SQL Having

Learn SQL Having with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-having.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT customer_id, COUNT(*) AS orders`	Selects columns/expressions.
`FROM orders`	Chooses the source table(s).
`GROUP BY customer_id`	Groups rows for aggregation.
`HAVING COUNT(*) >= 2;`	Filters groups after aggregation.

🏢Real-world

1Counts, totals, and averages for KPIs.
2Finding top customers/products by revenue.

⚠Common Mistakes

1Mixing non-aggregated columns without GROUP BY.
2Using WHERE instead of HAVING for aggregate filters.

✅Best Practices

1Group first, then filter aggregates with HAVING.
2Name aggregates with aliases (AS total_sales).

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 038

SQL Exists

Learn SQL Exists with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-exists.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT customer_name`	Selects columns/expressions.
`FROM customers c`	Chooses the source table(s).
`WHERE EXISTS (`	Filters rows before grouping.
`SELECT 1 FROM orders o WHERE o.customer_id = c.id`	Selects columns/expressions.
`);`	SQL statement line.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 039

SQL Any

Learn SQL Any with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-any.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT id, total_amount`	Selects columns/expressions.
`FROM orders`	Chooses the source table(s).
`WHERE total_amount > (SELECT AVG(total_amount) FROM orders);`	Filters rows before grouping.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 040

SQL All

Learn SQL All with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-all.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT id, total_amount`	Selects columns/expressions.
`FROM orders`	Chooses the source table(s).
`WHERE total_amount > (SELECT AVG(total_amount) FROM orders);`	Filters rows before grouping.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 041

SQL Select Into

Learn SQL Select Into with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-select-into.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`CREATE TABLE high_value_orders AS`	Creates a database object (table/view/index).
`SELECT * FROM orders WHERE total_amount > 500;`	Selects columns/expressions.
`SELECT COUNT(*) AS rows_in_new_table FROM high_value_orders;`	Selects columns/expressions.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 042

SQL Insert Into Select

Learn SQL Insert Into Select with a small query you can edit and run.

📝Syntax

INSERT INTO table (col1, col2)
VALUES (val1, val2);

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-insert-into-select.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`INSERT INTO customers (customer_name, city, country)`	Inserts new row(s).
`VALUES ('Zara', 'Dubai', 'UAE');`	SQL statement line.
`SELECT customer_name, country`	Selects columns/expressions.
`FROM customers`	Chooses the source table(s).
`ORDER BY id DESC`	Sorts the result set.
`LIMIT 3;`	Limits how many rows are returned.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 043

SQL Case

Learn SQL Case with a small query you can edit and run.

📝Syntax

SELECT col,
  CASE WHEN col > 0 THEN 'pos' ELSE 'non-pos' END AS label
FROM table;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-case.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT id, total_amount,`	Selects columns/expressions.
`CASE`	SQL statement line.
`WHEN total_amount >= 1000 THEN 'high'`	SQL statement line.
`WHEN total_amount >= 200 THEN 'medium'`	SQL statement line.
`ELSE 'low'`	SQL statement line.
`END AS bucket`	SQL statement line.
`FROM orders`	Chooses the source table(s).
`ORDER BY total_amount DESC;`	Sorts the result set.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 044

SQL Null Functions

Learn SQL Null Functions with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-null-functions.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT customer_name, COALESCE(city, 'Unknown') AS city`	Selects columns/expressions.
`FROM customers`	Chooses the source table(s).
`ORDER BY customer_name;`	Sorts the result set.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 045

SQL Stored Procedures

Learn SQL Stored Procedures with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-stored-procedures.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT 'Stored procedures demo (read note)' AS info;`	Selects columns/expressions.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 046

SQL Comments

Learn SQL Comments with a small query you can edit and run.

📝Syntax

-- single line
/* multi line */

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-comments.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`/* Multi-line`	SQL statement line.
`comment */`	SQL statement line.
`SELECT 1 AS one;`	Selects columns/expressions.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 047

SQL Operators

Learn SQL Operators with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-operators.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT 7 + 3 AS add, 7 * 3 AS mul, 7 > 3 AS is_greater;`	Selects columns/expressions.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 048

SQL Database

Learn SQL Database with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-database.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT 1 AS example;`	Selects columns/expressions.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 049

SQL Create DB

Learn SQL Create DB with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-create-db.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT 'Read the explanation for this topic.' AS note;`	Selects columns/expressions.

🏢Real-world

1Design tables with correct keys and constraints.
2Evolve schema with migrations.

⚠Common Mistakes

1Changing schema directly in production without a migration plan.
2Missing indexes on lookup/join columns.

✅Best Practices

1Use migrations + backups.
2Add constraints to enforce data integrity.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 050

SQL Drop DB

Learn SQL Drop DB with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-drop-db.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT 'Read the explanation for this topic.' AS note;`	Selects columns/expressions.

🏢Real-world

1Design tables with correct keys and constraints.
2Evolve schema with migrations.

⚠Common Mistakes

1Changing schema directly in production without a migration plan.
2Missing indexes on lookup/join columns.

✅Best Practices

1Use migrations + backups.
2Add constraints to enforce data integrity.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 051

SQL Backup DB

Learn SQL Backup DB with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-backup-db.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT 'Read the explanation for this topic.' AS note;`	Selects columns/expressions.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 052

SQL Create Table

Learn SQL Create Table with a small query you can edit and run.

📝Syntax

CREATE TABLE table (
  id INTEGER PRIMARY KEY,
  name TEXT NOT NULL
);

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-create-table.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`CREATE TABLE students (`	Creates a database object (table/view/index).
`id INTEGER PRIMARY KEY AUTOINCREMENT,`	SQL statement line.
`name TEXT NOT NULL,`	SQL statement line.
`marks INTEGER`	SQL statement line.
`);`	SQL statement line.
`INSERT INTO students (name, marks) VALUES ('Mia', 88), ('Noah', 72);`	Inserts new row(s).
`SELECT * FROM students;`	Selects columns/expressions.

🏢Real-world

1Design tables with correct keys and constraints.
2Evolve schema with migrations.

⚠Common Mistakes

1Changing schema directly in production without a migration plan.
2Missing indexes on lookup/join columns.

✅Best Practices

1Use migrations + backups.
2Add constraints to enforce data integrity.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 053

SQL Drop Table

Learn SQL Drop Table with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-drop-table.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`CREATE TABLE tmp_table (id INTEGER);`	Creates a database object (table/view/index).
`DROP TABLE tmp_table;`	Removes a database object.
`SELECT 'dropped tmp_table' AS status;`	Selects columns/expressions.

🏢Real-world

1Design tables with correct keys and constraints.
2Evolve schema with migrations.

⚠Common Mistakes

1Changing schema directly in production without a migration plan.
2Missing indexes on lookup/join columns.

✅Best Practices

1Use migrations + backups.
2Add constraints to enforce data integrity.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 054

SQL Alter Table

Learn SQL Alter Table with a small query you can edit and run.

📝Syntax

ALTER TABLE table ADD COLUMN new_col TEXT;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-alter-table.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`CREATE TABLE demo (id INTEGER);`	Creates a database object (table/view/index).
`ALTER TABLE demo ADD COLUMN name TEXT;`	Changes a table definition.
`PRAGMA table_info(demo);`	SQL statement line.

🏢Real-world

1Design tables with correct keys and constraints.
2Evolve schema with migrations.

⚠Common Mistakes

1Changing schema directly in production without a migration plan.
2Missing indexes on lookup/join columns.

✅Best Practices

1Use migrations + backups.
2Add constraints to enforce data integrity.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 055

SQL Constraints

Learn SQL Constraints with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-constraints.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`CREATE TABLE demo_users (`	Creates a database object (table/view/index).
`id INTEGER PRIMARY KEY AUTOINCREMENT,`	SQL statement line.
`name TEXT NOT NULL,`	SQL statement line.
`role TEXT NOT NULL DEFAULT 'user'`	SQL statement line.
`);`	SQL statement line.
`INSERT INTO demo_users (name) VALUES ('Aarav');`	Inserts new row(s).
`SELECT * FROM demo_users;`	Selects columns/expressions.

🏢Real-world

1Design tables with correct keys and constraints.
2Evolve schema with migrations.

⚠Common Mistakes

1Changing schema directly in production without a migration plan.
2Missing indexes on lookup/join columns.

✅Best Practices

1Use migrations + backups.
2Add constraints to enforce data integrity.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 056

SQL Not Null

Learn SQL Not Null with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-not-null.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`CREATE TABLE demo_users (`	Creates a database object (table/view/index).
`id INTEGER PRIMARY KEY AUTOINCREMENT,`	SQL statement line.
`name TEXT NOT NULL,`	SQL statement line.
`role TEXT NOT NULL DEFAULT 'user'`	SQL statement line.
`);`	SQL statement line.
`INSERT INTO demo_users (name) VALUES ('Aarav');`	Inserts new row(s).
`SELECT * FROM demo_users;`	Selects columns/expressions.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 057

SQL Unique

Learn SQL Unique with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-unique.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`CREATE TABLE demo_users (`	Creates a database object (table/view/index).
`id INTEGER PRIMARY KEY AUTOINCREMENT,`	SQL statement line.
`name TEXT NOT NULL,`	SQL statement line.
`role TEXT NOT NULL DEFAULT 'user'`	SQL statement line.
`);`	SQL statement line.
`INSERT INTO demo_users (name) VALUES ('Aarav');`	Inserts new row(s).
`SELECT * FROM demo_users;`	Selects columns/expressions.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 058

SQL Primary Key

Learn SQL Primary Key with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-primary-key.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`CREATE TABLE demo_users (`	Creates a database object (table/view/index).
`id INTEGER PRIMARY KEY AUTOINCREMENT,`	SQL statement line.
`name TEXT NOT NULL,`	SQL statement line.
`role TEXT NOT NULL DEFAULT 'user'`	SQL statement line.
`);`	SQL statement line.
`INSERT INTO demo_users (name) VALUES ('Aarav');`	Inserts new row(s).
`SELECT * FROM demo_users;`	Selects columns/expressions.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 059

SQL Foreign Key

Learn SQL Foreign Key with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-foreign-key.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`CREATE TABLE demo_users (`	Creates a database object (table/view/index).
`id INTEGER PRIMARY KEY AUTOINCREMENT,`	SQL statement line.
`name TEXT NOT NULL,`	SQL statement line.
`role TEXT NOT NULL DEFAULT 'user'`	SQL statement line.
`);`	SQL statement line.
`INSERT INTO demo_users (name) VALUES ('Aarav');`	Inserts new row(s).
`SELECT * FROM demo_users;`	Selects columns/expressions.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 060

SQL Check

Learn SQL Check with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-check.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`CREATE TABLE demo_users (`	Creates a database object (table/view/index).
`id INTEGER PRIMARY KEY AUTOINCREMENT,`	SQL statement line.
`name TEXT NOT NULL,`	SQL statement line.
`role TEXT NOT NULL DEFAULT 'user'`	SQL statement line.
`);`	SQL statement line.
`INSERT INTO demo_users (name) VALUES ('Aarav');`	Inserts new row(s).
`SELECT * FROM demo_users;`	Selects columns/expressions.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 061

SQL Default

Learn SQL Default with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-default.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`CREATE TABLE demo_users (`	Creates a database object (table/view/index).
`id INTEGER PRIMARY KEY AUTOINCREMENT,`	SQL statement line.
`name TEXT NOT NULL,`	SQL statement line.
`role TEXT NOT NULL DEFAULT 'user'`	SQL statement line.
`);`	SQL statement line.
`INSERT INTO demo_users (name) VALUES ('Aarav');`	Inserts new row(s).
`SELECT * FROM demo_users;`	Selects columns/expressions.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 062

SQL Index

Learn SQL Index with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-index.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`CREATE INDEX idx_orders_total ON orders(total_amount);`	Creates a database object (table/view/index).
`SELECT name, sql FROM sqlite_master WHERE type = 'index';`	Selects columns/expressions.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 063

SQL Auto Increment

Learn SQL Auto Increment with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-auto-increment.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`CREATE TABLE demo_ai (id INTEGER PRIMARY KEY AUTOINCREMENT, name TEXT);`	Creates a database object (table/view/index).
`INSERT INTO demo_ai (name) VALUES ('one'), ('two');`	Inserts new row(s).
`SELECT * FROM demo_ai;`	Selects columns/expressions.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 064

SQL Dates

Learn SQL Dates with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-dates.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT id, created_at`	Selects columns/expressions.
`FROM orders`	Chooses the source table(s).
`WHERE created_at >= '2026-02-01'`	Filters rows before grouping.
`ORDER BY created_at;`	Sorts the result set.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 065

SQL Views

Learn SQL Views with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-views.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`CREATE VIEW v_order_totals AS`	Creates a database object (table/view/index).
`SELECT id, total_amount FROM orders;`	Selects columns/expressions.
`SELECT * FROM v_order_totals ORDER BY total_amount DESC;`	Selects columns/expressions.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 066

SQL Injection

Learn SQL Injection with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-injection.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT 'Use prepared statements (see notes)' AS info;`	Selects columns/expressions.

🏢Real-world

1Secure logins/search endpoints using parameterized queries.
2Prevent SQL injection attacks.

⚠Common Mistakes

1String concatenation with user input.
2Logging full SQL with secrets.

✅Best Practices

1Always use prepared statements / parameters in app code.
2Validate and limit inputs.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 067

SQL Parameters

Learn SQL Parameters with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-parameters.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT customer_name FROM customers WHERE country = 'India';`	Selects columns/expressions.

🏢Real-world

1Secure logins/search endpoints using parameterized queries.
2Prevent SQL injection attacks.

⚠Common Mistakes

1String concatenation with user input.
2Logging full SQL with secrets.

✅Best Practices

1Always use prepared statements / parameters in app code.
2Validate and limit inputs.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 068

SQL Prepared Statements

Learn SQL Prepared Statements with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-prepared-statements.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT customer_name FROM customers WHERE country = 'India';`	Selects columns/expressions.

🏢Real-world

1Secure logins/search endpoints using parameterized queries.
2Prevent SQL injection attacks.

⚠Common Mistakes

1String concatenation with user input.
2Logging full SQL with secrets.

✅Best Practices

1Always use prepared statements / parameters in app code.
2Validate and limit inputs.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 069

SQL Hosting

Learn SQL Hosting with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-hosting.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT 'Read the explanation for this topic.' AS note;`	Selects columns/expressions.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 070

SQL References

Learn SQL References with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-references.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT customer_name, country FROM customers ORDER BY customer_name LIMIT 5;`	Selects columns/expressions.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 071

SQL Data Types

Learn SQL Data Types with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-data-types.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT customer_name, country FROM customers ORDER BY customer_name LIMIT 5;`	Selects columns/expressions.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 072

SQL Keywords

Learn SQL Keywords with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-keywords.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT customer_name, country FROM customers ORDER BY customer_name LIMIT 5;`	Selects columns/expressions.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 073

MySQL Functions

Learn MySQL Functions with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

mysql-functions.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT customer_name, country FROM customers ORDER BY customer_name LIMIT 5;`	Selects columns/expressions.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 074

SQL Server Functions

Learn SQL Server Functions with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-server-functions.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT customer_name, country FROM customers ORDER BY customer_name LIMIT 5;`	Selects columns/expressions.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 075

MS Access Functions

Learn MS Access Functions with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

ms-access-functions.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT customer_name, country FROM customers ORDER BY customer_name LIMIT 5;`	Selects columns/expressions.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

∙ Chapter 076

SQL Quick Ref

Learn SQL Quick Ref with a small query you can edit and run.

📝Syntax

statement;

⚡Example (Edit & Run)

Edit the SQL below and click Run. The output panel shows a table (for SELECT) or rows affected (for other statements).

sql-quick-ref.sql

📝 Edit Code

👁 Output

💡 Tip: start with SELECT *, then narrow the columns and add filters.

🔍Line-by-line

Line	Meaning
`SELECT customer_name, country FROM customers ORDER BY customer_name LIMIT 5;`	Selects columns/expressions.

🏢Real-world

1Reporting dashboards, analytics, and backend APIs read data with SQL.

⚠Common Mistakes

1Forgetting a WHERE clause in UPDATE/DELETE.

✅Best Practices

1Start with SELECT * then narrow columns + filters.

📖Summary & Practice

1Practice the query on sample data, then apply the same pattern to real tables.
2Read query output carefully and verify counts when joining/grouping.

💡Practice: answer the questions below, then modify the example to match your answers.

1Change one clause (WHERE/JOIN/GROUP BY) and predict the row count.
2Add a new column to SELECT and rename it with AS.
3Write the same query in a slightly different way and compare results.

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