谈NOT IN和Exists

Select count(1)
    From eemployee
    where status=1
    and eid not in (select eid from CBENEFIT_STATUS)

居然一条记录都没有？

是因为
select eid from CBENEFIT_STATUS 中eid为空

解决方法：

    1/ 改为select eid from CBENEFIT_STATUS where eid is not null    --  where eid is not null

    Select count(1)
        From eemployee
        where status=1
        and eid not in (select eid from CBENEFIT_STATUS where eid is not null)

    2/ select * from table1 A where not exists (SELECT * FROM table2 B where B.col1=A.col1) 

    Select count(1)
        From eemployee a
        where status=1
        and not exists (select 1 from CBENEFIT_STATUS b where a.eid = b.eid)

参考网址:
http://x-spirit.iteye.com/blog/615603