midSQL
What is a subquery?
Updated May 17, 2026
Short answer
A subquery is a query inside another query.
Deep explanation
Subqueries allow nesting SELECT statements to compute intermediate results.
Real-world example
Finding users who have placed orders.
Common mistakes
- Overusing subqueries instead of joins.
Follow-up questions
- What is correlated subquery?
- Are subqueries slow?