Question

I’ve got 2 tables. The first table is full of entries. The second table defines what categories that entry belongs to:

Table 1:

entry_id | title
       1 | Entry1
       2 | Entry2
       3 | Entry3

Table 2

entry_id | cat_id
       1 | 233
       1 | 234
       1 | 678
       2 | 235
       2 | 453
       2 | 21
       3 | 234
       3 | 233

I’m trying to select an entry with a single query of all posts belonging to multiple categories. For example, I want to return the entries belonging to category ids, 233 and 234. I believe this needs a subquery although I’m not quite sure. Any help anybody? 🙂

Answer 1

Try this:

select * from entity e
where exists (select * from category c where c.entry_id=e.entry_id AND c.cat_id=233)
  and exists (select * from category c where c.entry_id=e.entry_id AND c.cat_id=234)

This returns rows that belong to both 233 and 234 (this is how I read your question, anyway; I may have misunderstood the “belonging to multiple categories” part).