Answer
SQL join forms include inner, left outer, right outer, full outer, cross, and self joins. • Inner joins keep matches. • Outer joins preserve specified unmatched rows and fill the missing side with NULL. • Cross joins produce every row combination.
💡 SQL Example
SELECT * FROM a LEFT JOIN b ON b.a_id = a.id;
Result
All rows from a, with matching b rows when present
⚡ Quick Revision
Join types differ mainly in how they handle matches and unmatched rows.