sql效率问题
create table t (
id Varchar2(10) primary key,
dmid Varchar2(10),
sbh Varchar2(10)
)


crate table dm(
dmid Varchar2(10),
dmName Varchar2(10),
sbh Varchar2(10)
)

select * from t where dmid in ( '01 ', '02 ', '03 ') and t.sbh = '12345 '


select * from t where sbh = '12345 ' and exists(
select * from dm where t.dmid = dm.dmid
)

select * from t where dmid in( '01 ', '02 ', '03 ') and exists(
select * from dm where t.dmid = dm.dmid and sbh = '12345 '
)

select * from t where exists(
select * from dm where t.dmid = dm.dmid and sbh = '12345 ' and dmid in( '01 ', '02 ', '03 ')
)

select * from t where dmid t.sbh = '12345 ' and dmid= '01 '
union
select * from t where dmid t.sbh = '12345 ' and dmid= '02 '
union
select * from t where dmid t.sbh = '12345 ' and dmid= '03 '

如果t表和dm表都很大，那种写法效率高啊？高人看下嘛

[解决办法]
union 是有排序并且去除重复值的。
相对来说，exists一般比in快一些，

具体还要看sql的执行计划，谁的执行计划好，谁就是好sql
[解决办法]
没怎么看明白，不过我想你要的是这个
select /*+ use_hash(t,dm)*/
*
from t,dm
where t.dmid=dm.dmid
and dm.sbh= '12345 '
如果标很大的话，就加上提示
/*+ use_hash(t,dm)*/如果不是很大就不用了。