SQL for applying conditions to multiple rows in a join

Question

I think I found the answer to my question, I\'m just unsure of the syntax, I keep getting SQL errors.

Basically, I want to do the opposite of IN. Take this example:<

Answer 1

I would do exactly what you are doing first, because that gets a list of all users with 'tag1' and a list of all users with 'tag2', but in the same response obviously. So, we have to add some more:

Do a group by users (or users.id) and then having count(*) == 2. That will group duplicate users (which means those with both tag1 and tag2) and then the having-part will remove the ones with just one of the two tags.

This solution avoids adding yet another join-statement, but honestly I'm not sure which is faster. People, feel free to comment on the performance-part :)

EDIT: Just to make it easier to try out, here's the whole thing:

SELECT * 
FROM users INNER JOIN 
     tags ON tags.user_id = users.id 
WHERE tags.name = 'tag1' OR tags.name = 'tag2'
GROUP BY users.id
HAVING COUNT(*) = 2