Question

My question is this: Is it possible to output multiple rows when joining from the same table?
With this code for example, I would like it to output 2 rows, one for each table. Instead, what it does is gives me 1 row with all of the data.

SELECT t1.*, t2.* 
FROM table t1
JOIN table t2 
    ON t2.id = t1.oldId
WHERE t1.id = '1'

UPDATE
Well the problem that I have with the UNION/UNION ALL is this: I don’t know what the t1.oldId value is equal to. All I know is the id for t1. I am trying to avoid using 2 queries so is there a way I could do something like this:

SELECT t1.*
FROM table t1
WHERE t1.id = '1'

UNION

SELECT t2.*
FROM table t2
WHERE t2.id = t1.oldId

SAMPLE DATA

messages_users
id    message_id   user_id   box   thread_id   latest_id
--------------------------------------------------------
8     1            1         1     NULL        NULL
9     2            1         2     NULL        16
10    2            65        1     NULL        15
11    3            65        2     2           NULL
12    3            1         1     2           NULL
13    4            1         2     2           NULL
14    4            65        1     2           NULL
15    5            65        2     2           NULL
16    6            1         1     2           NULL

Query:
SELECT mu.id FROM messages_users mu
JOIN messages_users mu2 ON mu2.latest_id IS NOT NULL
WHERE mu.user_id = '1' AND mu2.user_id = '1' AND ((mu.box = '1' 
AND mu.thread_id IS NULL AND mu.latest_id IS NULL) OR mu.id = mu2.latest_id)

This query fixes my problem. But it seems the answer to my question is to not use a JOIN but a UNION.

Answer 1

You mean one row for t1 and one row from t2?

You’re looking for UNION, not JOIN.

select * from table where id = 1
union
select * from table where oldid = 1