--disable_warnings
DROP TABLE IF EXISTS t1,t2;
--enable_warnings

--disable_abort_on_error

CREATE TABLE t1 ( PNUM BIGINT, EMPNUM BIGINT, HOURS BIGINT );
CREATE TABLE t2 like t1;
INSERT INTO t1 VALUES(1,1,1), (12,12,12), (80,80,80);
INSERT INTO t1 VALUES(2,2,2);

# Only the second query is between parentheses  --> Error
SELECT PNUM FROM t1
UNION
(SELECT PNUM FROM t2);

# Both queries are between parentheses  --> OK
(SELECT PNUM FROM t1)
UNION
(SELECT PNUM FROM t2);

# Both queries between parentheses, second query contains UNION --> Error
(SELECT PNUM FROM t1)
UNION ALL
(SELECT PNUM FROM t2
UNION
SELECT PNUM FROM t1);

# slightly modified original NIST test case
SELECT PNUM,EMPNUM,HOURS
FROM t1
WHERE HOURS=12
UNION ALL
(SELECT PNUM,EMPNUM,HOURS
FROM t1
UNION
SELECT PNUM,EMPNUM,HOURS
FROM t1
WHERE HOURS=80)
ORDER BY 2,1;