SQL query that gives distinct results that match multiple columns

Question

Sorry, I couldn't provide a better title for my problem as I am quite new to SQL. I am looking for a SQL query string that solves the below problem.

Let's assume the following table:

DOCUMENT_ID |     TAG
----------------------------
   1        |   tag1
   1        |   tag2
   1        |   tag3
   2        |   tag2
   3        |   tag1
   3        |   tag2
   4        |   tag1
   5        |   tag3

Now I want to select all distinct document id's that contain one or more tags (but those must provide all specified tags). For example: Select all document_id's with tag1 and tag2 would return 1 and 3 (but not 4 for example as it doesn't have tag2).

What would be the best way to do that?

Regards, Kai

Answer 1

SELECT document_id
FROM table
WHERE tag = 'tag1' OR tag = 'tag2'
GROUP BY document_id
HAVING COUNT(DISTINCT tag) = 2

Edit:

Updated for lack of constraints...