Question

I have a n to m relationship in SQL like this:

Table A:

Id
 1
 2
 3

Table B:

Id  
 1    
 2
 3

Relationship table AB:

Id_A  Id_B
 1      1
 1      3
 2      3

This means the object at table A with Id 1 is related with the object at table B with Id 1, also A:1 with B:3 and A:2 with B:3.

Now, what I am trying to accomplish is to get all Ids from table A, that do not have a relation with B:1. This should return A:2 and A:3.

How can I accomplish that?

Answer 1

SELECT id
FROM TableA
EXCEPT
SELECT Id_A
FROM TableAB
WHERE Id_B=1

Or (If you need additional columns from TableA not shown)

SELECT a.id /*,a.foo, a.bar*/
FROM TableA a
WHERE NOT EXISTS(SELECT * 
                 FROM TableAB ab 
                 WHERE ab.Id_B=1 AND ab.Id_A=a.Id)