from 内的子查询，引发的查询问题
select *
from (select acc_id, max(tran_dt) tran_dt
from a
where tran_cd = '103'
group by acc_id) z
where exists (select null
from b
where b.acc_id = z.acc_id
and b.tran_dt = z.tran_dt);
直接查询得到结果为空
create table z as
select acc_id, max(tran_dt) tran_dt
from a
where tran_cd = '103'
group by acc_id;
先建临时表，在查询，得到结果
select *
from z
where exists (select null
from b
where b.acc_id = z.acc_id
and b.tran_dt = z.tran_dt);
--先留个痕迹，以后再查查什么问题
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