SQL subqueries
SQL subqueries explained
Subqueries are an important SQL pattern for filtering, comparing, and deriving values from other result sets. They are often used in real reporting and business logic.
Common subquery patterns
WHERE subqueries
Filter rows based on results returned by a nested query.
IN subqueries
Check whether a value exists in a set returned by another query.
EXISTS subqueries
Test whether a related row exists without necessarily returning data.
Correlated subqueries
Reference the outer query from inside the inner query, allowing row-by-row logic.
Derived tables
Use a nested query as a temporary table-like result for further processing.
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