ScalarSubquery

You can place a ScalarSubquery anywhere an Expression is permitted. A ScalarSubquery turns a SelectExpression result into a scalar value because it returns only a single row and column value.

The query must evaluate to a single row with a single column.

Sometimes also called an expression subquery.

Syntax

(Query)

Examples

-- avg always returns a single value, so the subquery is
-- a ScalarSubquery 
SELECT NAME COMM
FROM STAFF
(SELECT AVG(BONUS + 800)
 FROM EMPLOYEE
     WHERE COMM < 5000);
 -- Introduce a way of "generating" new data values,
-- using a query which selects from a VALUES clause (which is an 
alternate form of a fullselect). 
-- This query shows how a table can be derived called "X" having 
2 columns "R1" and "R2" and 1 row of data.
SELECT R1,R2 
    FROM (VALUES('GROUP 1','GROUP 2')) AS X(R1,R2);