使用not in和 not exists这两sql为啥结果不一样？
select b.* from tmp_ddn a,tmp_ddn b
where b.order_item_id = a.root_order_item_id and
not exists( select * from tmp_ddn_guoji where sn_97 = a.sn_97 )
and not exists( select * from tmp_ddn_vpn where sn_97 = a.sn_97 )
and not exists( select * from tmp_ddn_shangwang where sn_97 = a.sn_97 ))
和
select b.* from tmp_ddn a,tmp_ddn b
where b.order_item_id = a.root_order_item_id and
a.sn_97 not in ( select sn_97 from tmp_ddn_guoji )
and a.sn_97 not in ( select sn_97 from tmp_ddn_vpn )
and a.sn_97 not in ( select sn_97 from tmp_ddn_shangwang )
这两语句的意思应该相同吧？为什么结果不同？
[解决办法]
有空值是会不一样。
[解决办法]
sn_97 有空值
[解决办法]
如果不想选择出非空的部分，在第一语句中加 A.SN_97 IS NOT NULL 即可。
select b.* from tmp_ddn a,tmp_ddn b
where b.order_item_id = a.root_order_item_id and （A.SN_97 IS NOT NULL）
not exists( select * from tmp_ddn_guoji where sn_97 = a.sn_97 )
and not exists( select * from tmp_ddn_vpn where sn_97 = a.sn_97 )
and not exists( select * from tmp_ddn_shangwang where sn_97 = a.sn_97 ))
