ADVANCED

SQL Subqueries

Use the result of one query inside another query.

After this lessonFilter or compare rows using a nested query.

How it works

A subquery is a query nested inside another statement. It can return a single value, a list or a derived dataset depending on where it is used.

For clarity, start with a simple inner query and verify its output before embedding it. For repeated or complex logic, a CTE can often be easier to read.

REAL WORK

Find materials above average consumption, suppliers slower than the global average or orders containing exception items.

SYNTAX

The pattern

SELECT columns
FROM table
WHERE value > (SELECT AVG(value) FROM table);

Example

SELECT ProductName, Price
FROM Products
WHERE Price > (SELECT AVG(Price) FROM Products);

TRY IT

Run the example

Edit the query and run it against the built-in demo tables. Nothing is sent to a server.

SELECT ProductName, Price
FROM Products
ORDER BY Price DESC;

The learning runner supports SELECT, WHERE, LIKE, IN, BETWEEN, GROUP BY, HAVING, JOIN, aggregates, ORDER BY and LIMIT. Advanced lessons explain additional production SQL concepts even when the mini runner does not execute that syntax.

QUICK CHECK

Where can a scalar subquery be useful?

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