Subqueries

Subquery in WHERE

A subquery runs first and feeds its result into the outer query.

SELECT name FROM customers
WHERE id IN (
  SELECT customer_id FROM orders WHERE amount > 1500
);

Output:

name
Asha Rao

Scalar & correlated subqueries

A scalar subquery returns a single value; a correlated subquery references the outer query's row and re-runs for each one.