Question

I have a table with two columns, blog post ids and tag ids. A blog post can have several tags like it’s a post about “New York” and “Soho”. Let’s say I want to find all the blog posts that have BOTH tag id 1 and 2, how do I do that?

blogPostToTags
=============================
id           |tagId
-----------------------------
1            |1
1            |2
2            |1
3            |2

UPDATE:

I’ve tried the following:

SELECT id FROM blogPostToTags WHERE tagId = 1 AND tagId = 2

and

SELECT id FROM blogPostToTags WHERE tagId = 1 OR tagId = 2

neither work…

Answer 1

Use double JOIN.

SELECT id
FROM blogPosts p
INNER JOIN blogPostToTags pt1 ON pt1.id = p.id
INNER JOIN blogPostToTags pt2 ON pt2.id = p.id
WHERE pt1.tagId = 1 AND pt2.tagId = 2;