将分组应用于If语句结果

Question

Essentially, I have two tables:
Table A

aId|isOne|bId
---+-----+---
1  |1    |2
2  |0    |2
3  |1    |1

Table B

bId|one|two
---+---+---
1  |5  |13
2  |3  |11

Table A refers to Table B and specifies whether the data of one or of two is desired. What I need to do is sum the values given the bId , so the expected result of the query on these table would be:

bId|value
---+-----
2  |14
1  |5

Currently my query for doing this has the following form:

select bId, 
        coalesce(if(bId = 0, null, 
                    sum(if(isOne = 0, 
                           (select two from tableB where tableB.bId = bId),
                           (select one from tableB where tableB.bId = bId)))) as value 
from (select bId, isOne, one, two from tableA 
      join tableB on tableA.bId = tableB.bId) as tableRes;

Please note that this is in relaity part of a larger query and uses larger tables, where the coalesce and first if statement do make sense to use.

An error occurs with the above query though (

Error Code: 1242. Subquery returns more than 1 row)

which is believed to come from the if statement within sum() . I have tried applying group by , since I think I need to group the bId = 2 value results together, but have failed to be able to place this legally, or place it legally within the query and have it actually stop the subqueries from returning more than one result. Any direction or help in fixing the error would be appreciated, also may good to know that as stated, this is a stripped down version of the query, so if it is thought the problem is not in what has been shown more can be added, but I'm pretty confident in the error lying in the above version.

Answer 1

I would simply inner join the 2 tables and use case statement within the sum() to sum the right values:

select tableA.bId, sum(case when isOne=0 then two when isOne=1 then one else 0 end) as val
from tableA 
inner join tableB on tableA.bId = tableB.bId
group by tableA.bId ;

Answer 2

You don't need such a complicated structure, just do the sums in the join.

SELECT tableA.bId, SUM(IF(isOne, one, two)) AS value
FROM tableA
JOIN tableB ON tableA.bId = tableB.bId
GROUP BY tableA.bId

Answer 3

实际上，对于任何对答案感到好奇的人，我都可以用指定的tableA.bId值替换子查询中的任意bId来解决此问题。