Question

I have a table that looks like so:

+-----+--------------+---------+----------+---------------------+---------------------+
| id  | username     | case_id | status   | date_assigned       | date_removed        |
+-----+--------------+---------+----------+---------------------+---------------------+
|  21 | hemcreynolds | 802     | inactive | 2007-08-20 07:15:48 | 2008-04-15 16:08:54 |
| 133 | licox        | 868     | active   | 2007-09-02 11:55:37 | 0000-00-00 00:00:00 |
|   3 | kashepherd   | 794     | inactive | 2007-08-17 13:54:39 | 2010-08-12 14:40:37 |
|   4 | tithomas     | 795     | active   | 2007-08-17 13:56:06 | 0000-00-00 00:00:00 |
|   5 | stcosse      | 795     | inactive | 2007-08-17 13:56:26 | 2007-09-25 10:02:03 |
|   6 | mefong yit   | 914     | active   | 2007-08-17 14:00:29 | 0000-00-00 00:00:00 |
|   7 | tamouledoux  | 842     | active   | 2007-08-17 14:09:16 | 0000-00-00 00:00:00 |
|   9 | chgross      | 903     | active   | 2007-08-18 08:38:38 | 0000-00-00 00:00:00 |
|  20 | ticrane      | 802     | inactive | 2007-08-20 07:15:41 | 2008-04-15 16:44:35 |
|  19 | hemcreynolds | 818     | inactive | 2007-08-20 07:15:12 | 2008-04-15 16:08:57 |
+-----+--------------+---------+----------+---------------------+---------------------+

I’d like to run a query to find which cases a user has been assigned to by username, e.g.

SELECT username,case_id from assignments WHERE username = 'ticrane'

I would then like to find all the other users assigned to the cases that my user (ticrane) is assigned to:

 SELECT * FROM assignements WHERE case_id = (all of the case ids generated by the previous query)

I’d like to do this in a single query. I imagine that some kind of join is in order here, but I don’t think you can join results from the same table. Confused. Any suggestions?

Answer 1

It is perfectly legal to join a table to itself, but you need to give an alias to at least one of the two “copies” of the table so that the statement is not ambiguous.

SELECT
    assignments_join.*
FROM
    assignments AS assignments_base
    JOIN assignments AS assignments_join ON
        assignments_base.case_id = assignments_join.case_id
WHERE
    assignments_base.username = 'ticrane'