SQL中EXCEPT和Not in的区别?
2014-04-03 09:40
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初始化两张表:
CREATE TABLE tb1(ID int)
INSERT tb1 SELECT NULL
UNION ALL SELECT NULL
UNION ALL SELECT NULL
UNION ALL SELECT 1
UNION ALL SELECT 2
UNION ALL SELECT 2
UNION ALL SELECT 2
UNION ALL SELECT 3
UNION ALL SELECT 4
UNION ALL SELECT 4
CREATE TABLE tb2(ID int)
INSERT tb2 SELECT NULL
UNION ALL SELECT 1
UNION ALL SELECT 3
UNION ALL SELECT 4
UNION ALL SELECT 4
A:
SELECT * FROM tb1
SELECT * FROM tb2
SELECT * FROM tb1 EXCEPT SELECT * FROM tb2;
SELECT * FROM tb1 WHERE id NOT IN(SELECT id FROM tb2);--得不到任何值
结果:
B、我先删除表tb1的是NULL值的行
--DELETE FROM tb1 where id is null
B、
SELECT * FROM tb1 EXCEPT SELECT * FROM tb2;
SELECT * FROM tb1 WHERE id NOT IN(SELECT id FROM tb2);--得不到任何值
结果:同上A
C、把表tb2的是NULL值的行也删除
--DELETE FROM tb2 where id is null
C、
SELECT * FROM tb1 EXCEPT SELECT * FROM tb2;
SELECT * FROM tb1 WHERE id NOT IN(SELECT id FROM tb2);
结果:
这是两张表中都没有NULL值时,得到的结果;
D、在tb1表中插入一条NULL值
D、
SELECT * FROM tb1 EXCEPT SELECT * FROM tb2;
SELECT * FROM tb1 WHERE id NOT IN(SELECT id FROM tb2);
结果:
以上例子说明:
except会去重复, not in 不会(除非你在select中显式指定)
except用于比较的列是所有列, 除非写子查询限制列, not in 没有这种情况
表tb2中如果有null值的话,not in查询得不到值(如:A、B)
表tb1中如果有null值,not in不会查询出这个null值(如:D),而except可以查询到
当然通过对子查询指定不为NULL的话,NOT IN自然会得到值,如:
SELECT * FROM tb1 WHERE id NOT IN(SELECT id FROM tb2 WHERE ID IS NOT NULL);
CREATE TABLE tb1(ID int)
INSERT tb1 SELECT NULL
UNION ALL SELECT NULL
UNION ALL SELECT NULL
UNION ALL SELECT 1
UNION ALL SELECT 2
UNION ALL SELECT 2
UNION ALL SELECT 2
UNION ALL SELECT 3
UNION ALL SELECT 4
UNION ALL SELECT 4
CREATE TABLE tb2(ID int)
INSERT tb2 SELECT NULL
UNION ALL SELECT 1
UNION ALL SELECT 3
UNION ALL SELECT 4
UNION ALL SELECT 4
A:
SELECT * FROM tb1
SELECT * FROM tb2
SELECT * FROM tb1 EXCEPT SELECT * FROM tb2;
SELECT * FROM tb1 WHERE id NOT IN(SELECT id FROM tb2);--得不到任何值
结果:
B、我先删除表tb1的是NULL值的行
--DELETE FROM tb1 where id is null
B、
SELECT * FROM tb1 EXCEPT SELECT * FROM tb2;
SELECT * FROM tb1 WHERE id NOT IN(SELECT id FROM tb2);--得不到任何值
结果:同上A
C、把表tb2的是NULL值的行也删除
--DELETE FROM tb2 where id is null
C、
SELECT * FROM tb1 EXCEPT SELECT * FROM tb2;
SELECT * FROM tb1 WHERE id NOT IN(SELECT id FROM tb2);
结果:
这是两张表中都没有NULL值时,得到的结果;
D、在tb1表中插入一条NULL值
D、
SELECT * FROM tb1 EXCEPT SELECT * FROM tb2;
SELECT * FROM tb1 WHERE id NOT IN(SELECT id FROM tb2);
结果:
以上例子说明:
except会去重复, not in 不会(除非你在select中显式指定)
except用于比较的列是所有列, 除非写子查询限制列, not in 没有这种情况
表tb2中如果有null值的话,not in查询得不到值(如:A、B)
表tb1中如果有null值,not in不会查询出这个null值(如:D),而except可以查询到
当然通过对子查询指定不为NULL的话,NOT IN自然会得到值,如:
SELECT * FROM tb1 WHERE id NOT IN(SELECT id FROM tb2 WHERE ID IS NOT NULL);
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