TableSubquery

A TableSubquery is a subquery that returns multiple rows.

Unlike a ScalarSubquery, a TableSubquery is allowed only:

as a TableExpression in a FROM clause
with EXISTS, IN, or quantified comparisons.

When used as a TableExpression in a FROM clause, it can return multiple columns. When used with EXISTS, it returns multiple columns only if you use * to return the multiple columns.

When used with IN or quantified comparisons, it must return a single column.

Syntax

(Query)

-- a subquery used as a TableExpression in a FROM clause
SELECT VirtualFlightTable.flight_ID
FROM
    (SELECT flight_ID, orig_airport, dest_airport
    FROM Flights
    WHERE (orig_airport = 'SFO' OR dest_airport = 'SCL') )
AS VirtualFlightTable
-- a subquery (values expression) used as a TableExpression
-- in a FROM clause
SELECT mycol1
FROM
    (VALUES (1, 2), (3, 4))
AS mytable (mycol1, mycol2)
-- a subquery used with EXISTS
SELECT *
FROM Flights
WHERE EXISTS
    (SELECT * FROM Flights WHERE dest_airport = 'SFO'
    AND orig_airport = 'GRU')
-- a subquery used with IN
SELECT flight_id, segment_number
FROM Flights
WHERE flight_id IN
    (SELECT flight_ID
    FROM Flights WHERE orig_airport = 'SFO'
    OR dest_airport = 'SCL')
-- a subquery used with a quantified comparison
SELECT NAME, COMM 
FROM STAFF 
WHERE COMM > 
(SELECT AVG(BONUS + 800)
     FROM EMPLOYEE
     WHERE COMM < 5000);