Subquery

How it is used

Also called an inner or nested query. Subqueries appear in WHERE (… IN (SELECT …)), in FROM as a derived table, or in the SELECT list. A correlated subquery refers to the outer query and runs once per row, which can be slow; a join or CTE is often clearer.

Example sentences

1. The subquery returns the IDs of customers who ordered last month.

2. Rewriting the correlated subquery as a join cut the run time in half.

Common collocations

• correlated subquery
• nested subquery
• subquery in the WHERE clause
• rewrite a subquery

Related terms

• queryA request sent to a database to read or change data, usually written in SQL. As a verb, to query means to ask a database for data.
• CTECommon table expression: a named temporary result defined with WITH at the start of a query, which the main query can then use like a table.
• joinA SQL operation that combines rows from two or more tables using a related column, such as a customer ID. As a verb, to join tables means to combine them this way.
• SELECT statementThe SQL statement that reads data from one or more tables and returns the matching rows without changing anything in the database.

This word in other fields

The same English word can have a different meaning in another field:

• subquery · Software Engineering

More terms: SQL Statements and Queries

• SQL
• WHERE clause
• INSERT statement
• UPDATE statement
• DELETE statement
• ORDER BY
• GROUP BY
• aggregate function
• inner join
• left join
• HAVING clause
• SELECT DISTINCT