浅析被遗忘的SQLServer比较运算符修饰词

SQLServer中有三个关键字可以修改比较运算符：All、Any和Some，其中Some和Any等价。


官方的参考文档
http://technet.microsoft.com/zh-cn/library/ms187074%28SQL.90%29.aspx

他们作用于比较运算符和子查询之间，作用类似Exists、not exists、in、not in以及其他逻辑意义，这些语法同样被SQLServer2000支持但是很少看到有人用它们。


复制代码 代码如下:

set nocount on

use tempdb

go

if (object_id (‘t1’ ) is not null ) drop table t1

create table t1 (n int )

insert into t1 select 2 union select 3  

if (object_id (‘t2’ ) is not null ) drop table t2

create table t2 (n int )

insert into t2 select 1 union select 2 union select 3 union select 4

select * from t2 where n> all (select n from t1 )    –4

select * from t2 where n> any (select n from t1 )    –3,4

–select * from t2 where n>some(select n from t1)    –3,4

select * from t2 where n= all (select n from t1 )    –无数据

select * from t2 where n= any (select n from t1 )    –2,3

–select * from t2 where n=some(select n from t1) –2,3

select * from t2 where n< all (select n from t1 )    –1

select * from t2 where n< any (select n from t1 )    –1,2

–select * from t2 where n<some(select n from t1)    –1,2

select * from t2 where n<> all (select n from t1 )    –1,4

select * from t2 where n<> any (select n from t1 )    –1,2,3,4

–select * from t2 where n<>some(select n from t1)–1,2,3,4

set nocount off

注意，如果t1中包含null数据，那么所有All相关的比较运算将不会返回任何结果，原因就不用多解释了。而因为t1和t2表的null的存在他们和not exists之类的比较符会有一些区别。

比如下面两句

select * from t2 a where not exists(select 1 from t1 where n>=a.n)
select * from t2 where  n >all(select n from t1)
他们逻辑上意义很像但是对于null的处理却是恰恰相反，第一句会忽略子查询的null而把t2的null同时查出来，第二句却是忽略了t2的null同时会因为t1中的null而无法查询到数据。