小编Liz*_*zie的帖子

MINUS运营商

我有2张桌子A和B.

SELECT COUNT(*) FROM (SELECT * FROM tableA)

返回389

SELECT COUNT(*) FROM (SELECT * FROM tableB)

返回217

SELECT COUNT(*) FROM
(SELECT * FROM tableA
INTERSECT
SELECT * FROM tableB)

返回0

SELECT COUNT(*) FROM 
(SELECT * FROM tableA
MINUS
SELECT * FROM tableB)

返回389

SELECT COUNT(*) FROM 
(SELECT * FROM tableB
MINUS
SELECT * FROM tableA)

返回89

有人可以解释为什么最后一个查询返回89而不是217？