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A subquery is a SELECT statement within another statement. is a SQL query nested inside a larger query.

Here is an example of a subquery:

SELECT * FROM t1 WHERE column1 = (SELECT column1 FROM t2);

In this example, SELECT * FROM t1 ... is the outer query (or outer statement), and (SELECT column1 FROM t2) is the subquery. We say that the subquery is nested within the outer query, and in fact it is possible to nest subqueries within other subqueries, to a considerable depth. A subquery must always appear within parentheses.

The main advantages of subqueries are:

  • They allow queries that are structured so that it is possible to isolate each part of a statement.

  • They provide alternative ways to perform operations that would otherwise require complex joins and unions.

  • Many people find subqueries more readable than complex joins or unions.

A subquery may occur in:

  • A SELECT clause
  • A FROM clause
  • A WHERE clause

For more information, see the reference below:


MatrixOne does not support selecting multiple columns for the subquery.