如何在配置单元查询中编写 case 和 group by

Question

这是我的蜂巢table:

course   dept    subject   status

btech     cse     java     pass
btech     cse     hadoop   fail
btech     cse     cg       detained
btech     cse     cc       pass
btech      it     daa      pass
btech      it     wt       pass
btech      it     cnn      pass
mba        hr     hrlaw    pass
mba        hr     hrguid   absent
mtech      cs     java     pass
mtech      cs     cd       pass
mtech      cs     cp       detained

我想查询此 table 以通过以下方式检索数据：

course   dept    status

btech     cse     fail
btech      it     pass
mba        hr     absent
mtech      cs     fail

首先，它会检查每个 dept 和 course 组合在一起的 status 中的 "fail" 或 "detained"。如果找到 "fail" 或 "detained"，它将输出 "fail" 作为 status。否则，如果在同一组中发现 "absent"，它将输出 "absent" 作为 status。否则，它将输出 "pass".

我在运行以下查询时收到一条错误消息：

select course,dept,
case 
when status in ( 'fail','detained') then 'fail'
when status in ( 'absent') then 'absent'
when status in ( 'pass') then 'pass'
else null 
end as Final_Status
from college
group by course,dept;

Answer 1

问题是，group by所需的列需要放在最后。在修改后的查询下方，它现在应该可以工作了。

select 
case 
when status in ( 'fail','detained') then 'FAILED'
when status in ( 'absent') then 'absent'
when status in ( 'pass') then 'PASSED'
else null 
end as Final_Status,course,dept
from college
group by course,dept;

Answer 2

当你按课程和部门分组时，你会得到状态列的多个值（针对不同的记录），这需要处理。
select 中的任何列是不是 group by 的一部分应该在聚合函数中
这是一个使用 sum() 函数的解决方案。

select course, dept,
    case when sum(case when status in ( 'fail','detained') then 1 else 0 end) > 0 then 'fail'
         when sum(case when status in ('absent') then 1 else 0 end) > 0 then 'absent'
         when sum(case when status in ('pass') then 1 else 0 end) > 0 then 'pass'
         else 'no_result'
    end as final_status
from college
group by 
    course,dept

Answer 3

试试这个。

select course,dept,
collect_set(
case 
when status in ( 'fail','detained') then 'FAILED'
when status in ( 'absent') then 'absent'
when status in ( 'pass') then 'PASSED'
else null 
end ) as Final_Status
from college
group by course,dept;

Answer 4

如果我没理解错的话，你想要这样的东西：

select course,dept,
case 
when status in ( 'fail','detained') then 'FAILED'
when status in ( 'absent') then 'absent'
when status in ( 'pass') then 'PASSED'
else null 
end as Final_Status
from college
group by course,dept, 
   CASE when status in ( 'fail','detained') then 'FAILED'
   when status in ( 'absent') then 'absent'
   when status in ( 'pass') then 'PASSED'
   else null END;

我在 GROUP 中使用 CASE，它与 Hive 配合得很好。

如何在配置单元查询中编写 case 和 group by

how to write case and group by in hive query

hadoop

hive

hiveql