检索 a 列值，其中主键是元组 (a,b) 并且对于 b' 值的给定列表必须存在所有行 (a,b')

Question

I have a table of form A|B|C where a tuple (a,b) in (A,B) is the primary key. I have list of values (BVALs) for B and I require the elements in the column A where a row entry for each value of the type (a,b') for b' in BVALs exists.

Currently I have implemented a script that retrieves the first all (a,b'') for the first element of the BVALs, which then iterates and refines the list until the last element of the BVALs. I believe it will be slow in big databases and believe that an faster solution exists. Would appreciate any help.

Let's say we have the following table:

+---+---+
| A | B |
+---+---+
| 1 | 1 |
| 1 | 2 |
| 1 | 3 |
| 1 | 4 |
| 2 | 1 |
| 2 | 2 |
| 3 | 1 |
+---+---+

If the BVALs list consists of (1,2) then the query should return 1 and 2

Answer 1

I understand that you want a s that have all b values. If so, you can use group by and having :

select a
from mytable
where b in (1, 2)   -- either value
group by a
having count(*) = 2 -- both match 

Answer 2

Is this what you want?

select distinct a
from t
where b in ( . .  . );  -- list of b values here