Sql Subqueries — Free Sql Tutorial

TL;DR: Learn Sql Subqueries in Sql with a free, beginner-friendly tutorial, examples and practice for Indian students on Syllab.in.

Sql Subqueries in Sql

A subquery (also called a nested query or inner query) is a SQL query written inside another query. The inner query runs first, and its result is used by the outer query.

Subqueries can appear in: WHERE (most common — "find students who scored above the class average"), FROM (treat a query result as a table), SELECT (calculate a value for each row).

Correlated subquery: The inner query references a column from the outer query — it runs once for each row of the outer query. These can be slow but are very powerful.

-- Scalar (one value):
SELECT name FROM students
WHERE marks > (SELECT AVG(marks) FROM students);

-- Multi-row (IN):
WHERE class_id IN (SELECT class_id FROM classes WHERE section='A');

-- Exists:
WHERE EXISTS (SELECT 1 FROM awards WHERE student_id = s.student_id);

-- Derived table (subquery in FR

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