将查询的多行结果作为值添加到另一个查询

Question

I have a problem to solve, that requires me to select multiple values from two tables. From table BI need the values of 3 rows that reference to a key column from table A.

From what I found online I got the feeling, that this seems to come down to nested or recursive/hierarchial selects. But I can't figure out how to build the actual query with my different conditions between table A and B...

Given are tables like that:

Table A
ID | Val1 | Val2
----------------
01 | QWER | WERT
02 | ASDF | SDFG
...| ...  | ...

Table B
ID | Pos | ... | Val5
---------------------
01 | 001 | ... | X
01 | 002 | ... | Y
01 | 003 | ... | F
02 | 001 | ... | J
02 | 002 | ... | R
...| ... | ... | ...

Column ID is obviously the reference value between A and B.

I need to build a query like this:

ID | Val1 | Val2 | Val5 at B.Pos 001 | Val5 at B.Pos 002 | Val5 at B.Pos 003

I wasn't able to create a query as follows due to the multiple conditions between A and B and result in a "right bracket missing" error:

select 
  A.ID, 
  A.Val1,
  A.Val2,
  (select B.Val5 from B where B.ID = A.ID and B.Pos = 001),
  (select B.Val5 from B where B.ID = A.ID and B.Pos = 002),
  (select B.Val5 from B where B.ID = A.ID and B.Pos = 003)
from A

Is there a way to do this? It's a case I never encountered before, so I am lost...

Answer 1

Is this what you want?

select a.id, a.val1, a.val2,
       max(case when b.pos = 1 then b.val5 end) as bval1,
       max(case when b.pos = 2 then b.val5 end) as bval2,
       max(case when b.pos = 3 then b.val5 end) as bval3
from a join
     b
     on a.id = b.id
group by a.id, a.val1, a.val2;