Question

I’m having trouble forming my query for a user assessment table I have.

Currently the table looks like this.

+-----+----------+----------+
| id  | video_id | user_id  |
+-----+----------+----------+
| 1   |       1  |        1 |
| 2   |       2  |       50 |
| 3   |       1  |      115 |
| 4   |       2  |       25 |
| 5   |       2  |       1  |
| 6   |       6  |       98 |
| 7   |       3  |        1 |
+-----+----------+----------+

The issue I’m running into is forming a query that returns the user_id for someone who has watched video_id’s of 1, 2, and 3. So in the above example, only user_id 1 should be returned.

I thought doing something like

SELECT user_id 
    FROM user_assessment 
    WHERE video_id = '1' AND video_id = '2' AND video_id = '3'

but that clearly is incorrect.

Any help would be appreciated.

Answer 1

The key here is that the value checked in the HAVING clause (3) is equal to the number of elements contained within the IN grouping. This guarantees that all three videos are included.

SELECT user_id
    FROM user_assessment
    WHERE video_id IN (1, 2, 3)
    GROUP BY user_id
    HAVING COUNT(DISTINCT video_id) = 3