Retrieve multiple sum columns of sub queries

问题

From this query :

    select LastStateS='LastStateS1and2'
      , count(s.LastState) as sumS,
    LasteStateE='LastStateE1and2'
      , count(e.LastState) as sumE
from table1 t1
    join table2 t2
        on t1.ID = t2.ID
    join (select LastState
                ,count(LastState) as sum
          from table1
          where ID = X
            and LastState = 1
             or LastState = 2
          group by LastState
         ) s

        on s.LastState = t1.LastState
    join (select LastState
                ,count(LastState) as sum
          from table1
          where ID = X
            and LastState = 3
             or LastState = 4
          group by LastState
         ) e

        on e.LastState = t1.LastState

I can't retrieve the sum of both my "laststate" condition. All I have as result is my two columns empty. Thanks in advance.

回答1:

I am not sure why you are doing some things in this query that are not used, like count(LastState) in your sub-queries.

I think this is all you need for the results you are looking for:

select 
      LastStateS ='1 and 2'
    , countS = sum(case when t1.LastState in (1,2) then 1 else 0 end)
    , LasteStateE ='3 and 4'
    , countE = sum(case when t1.LastState in (3,4) then 1 else 0 end)
  from table1 t1
    inner join table2 t2 on t1.id = t2.id and t1.id = X

To get your original query to return the results you want, you need to use left joins for the subqueries:

select 
    LastStateS='LastStateS1and2'
  , count(s.LastState) as sumS
  , LasteStateE='LastStateE1and2'
  , count(e.LastState) as sumE
from table1 t1
  inner join table2 t2 on t1.ID = t2.ID
  left join (
    select 
        LastState
      , count(LastState) as sum
      from table1
      where ID = X
        and LastState = 1
         or LastState = 2
      group by LastState
     ) s
    on s.LastState = t1.LastState
  left join (
    select 
        LastState
      , count(LastState) as sum
      from table1
      where ID = X
        and LastState = 3
         or LastState = 4
      group by LastState
     ) e
    on e.LastState = t1.LastState

Also note, as @WEI_DBA points out in their comment, you may have unintended consequences from using where ID = X and LastState = 3 or LastState = 4 instead of where ID = X and (LastState = 3 or LastState = 4).

来源：https://stackoverflow.com/questions/41746714/retrieve-multiple-sum-columns-of-sub-queries