Question

I have this cross_reference table,

post_id | cat_id
-----------------
3          11
-----------------
3          2
-----------------
4          5
-----------------
4          6
-----------------
4          2
-----------------
5          8
-----------------
5          13

The problem is that this query does not return anything….

SELECT DISTINCT post_id FROM posts_categories WHERE cat_id = 11 AND cat_id = 2

I expect it to return ‘3’…

What am I doing wrong?

Answer 1

It is actually OR, not AND. Or better:

SELECT DISTINCT post_id FROM posts_categories WHERE cat_id IN (11,2);

Though I’d expect it to return 3 and 4.

UPDATE: (based on the comment)

SELECT post_id
FROM post_categories WHERE cat_id IN (2,12)
GROUP BY post_id HAVING count(*)=2;