Question

I have the following table structures.

Table A

id    name
1     name1
2     name2

Table B

a_id   b_id
1      1
1      2

How can I select all rows of table A that have both a b_id of 1 and 2? Table B is a mapping table between table A and another table, whose contents do not matter for this question.

Thank you for your time and help!

Answer 1

This query uses COUNT(DISTINCT) to ensure the presence of both values. If I did not use DISTINCT it may incorrectly count rows in TableB that look like this as a match when it shouldn’t:

a_id   b_id
1      1
1      1  


select a.id, a.name
from TableA a
inner join (
    select a_id
    from TableB
    where b_id in (1, 2)
    group by a_id
    having count(distinct b_id) = 2 #this number matches no. of unique values in IN clause
) b on a.id = b.a_id

SQL Fiddle example