这些子查询在oracle和mysql等数据库中都能执行，但是在hive中却不支持，但是我们可以把这些查询语句改为join操作：

--  1.子查询

select

    *

from

    A a

where

    a.update_time = (select min(b.update_time) from A b)

--  2.in操作

select

    *

from

    A a

where

    a.dept = 'IT'

and

    a.num in (select b.num from B b where b.flag = '') 

改为join操作如下：

--

select

    t2.*

from

    (select min(a.update_time) upt from A a) t1

left outer join

    (select b.* from A b) t2

on

    t1.upt = t2.update_time

--

select

    a.*

from

    A a

left semi join

    B b

on (a.num = b.num and a.dept = 'IT' and b.flag = '')

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原文：https://blog.csdn.net/qq_20641565/article/details/52851700