- A subquery is a SQL query within a query.
- Subqueries are nested queries that provide data to the enclosing query.
- Subqueries can return individual values or a list of records
- Subqueries must be enclosed with parenthesis
- A subquery cannot be immediately enclosed in a set function.
- You can place the Subquery in a number of SQL clauses: WHERE clause, HAVING clause, FROM clause.
Subqueries can be used with SELECT, UPDATE, INSERT, DELETE statements along with expression operator. It could be equality operator or comparison operator such as =, >, =, <= and Like operator.
- Subquery must be enclosed in parentheses.
- A subquery is a query within another query. The outer query is called as main query and inner query is called as subquery.
- The subquery generally executes first, and its output is used to complete the query condition for the main or outer query.
- An ORDER BY command cannot be used in a subquery, although the main query can use an ORDER BY. The GROUP BY command can be used to perform the same function as the ORDER BY in a subquery.
- Subqueries can return individual values or a list of records.
There is not any general syntax for Subqueries are regular queries placed inside parenthesis.
Subqueries are seen to be used most frequently with SELECT statement as shown below:
Here is an subquery with the IN operator.
Subqueries can also assign column values for each record:
SQL Subquery Examples
Problem: List products with order quantities greater than 100.