Answer
A composite index indexes more than one column in a defined order. • It can support queries using its leading columns. • Column order affects which predicates and orderings it can serve efficiently. • Duplicate indexes should be avoided because each adds maintenance cost.
💡 SQL Example
CREATE INDEX orders_customer_date_idx ON orders (customer_id, ordered_at);
Result
CREATE INDEX
⚡ Quick Revision
A composite index uses an ordered list of columns.