SQL query at least one of something

Question

I have a bunch of Users, each of whom has many Posts. Schema:

Users: id
Posts: user_id, rating

How do I find all Users who have at least one po

Answer 1

The correct answer for your question as stated is OMG Ponies's answer, WHERE EXISTS is more descriptive and almost always faster. But "SELECT NULL" looks really ugly and counterintuitive to me. I've seen SELECT * or SELECT 1 as a best practice for this.

Another way, in case we're collecting answers:

SELECT u.id 
FROM users u 
     JOIN posts p on u.id = p.user_id
WHERE p.rating > 10
GROUP BY u.id
HAVING COUNT(*) > 1

This could be useful if it's not always 1 you're testing on.