oracle exists查询慢,Oracle exists查询未按预期工作-数据库链接错误?

我对这个查询的结果感到非常困惑:

select count(*) from my_tab mt

where mt.stat = '2473'

and mt.name= 'Tom'

and exists (select * from [email protected] cu,

[email protected] pr

where cu.user_id = pr.user_id

and mt.name = pr.name

and mt.stat = cu.stat

)

收益率:1

在[email protected]中有0条stat='2473'的记录,那么为什么它会为exists返回true?

如果我这样更改查询,它将返回0:

select count(*) from my_tab mt

where mt.stat = '2473'

and mt.name= 'Tom'

and exists (select * from [email protected] cu,

[email protected] pr

where cu.user_id = pr.user_id

and mt.name = pr.name

and cu.stat = '2473'

)

更新

好吧,这真的很奇怪。为了看看会发生什么,我从另一个数据库(数据库链接引用的数据库)执行了查询,它给出了不同的(正确的)结果。

select count(*) from [email protected] mt

where mt.stat = '2473'

and mt.name= 'Tom'

and exists (select * from company_users cu,

personnel_records pr

where cu.user_id = pr.user_id

and mt.name = pr.name

and mt.stat = cu.stat

)

返回0(如预期)。