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5.2.1.3 Subqueries

Subqueries specifying a derived table must be enclosed in parentheses and must be assigned a table alias name. (See section 5.2.1.2 Table and Column Aliases.) For example:

FROM (SELECT * FROM table1) AS alias_name

This example is equivalent to FROM table1 AS alias_name. More interesting cases, which can't be reduced to a plain join, arise when the subquery involves grouping or aggregation.

A subquery can also be a VALUES list:

FROM (VALUES ('anne', 'smith'), ('bob', 'jones'), ('joe',
 'blow')) AS names(first, last)

Again, a table alias is required. Assigning alias names to the columns of the VALUES list is optional, but is good practice. For more information see section 5.7 VALUES Lists.