Question

So basically I have two tables:

u_contracts

+--------+---------+------------------------------+
| id     | user_id | reschedule_wait_confirm_till |
+--------+---------+------------------------------+
| 107742 |   19982 | 2012-08-08 17:10:41          |
|  38548 |    4622 | 2012-08-08 10:24:42          |
|  98483 |   36707 | 2012-08-08 21:39:08          |
|  45165 |   17632 | 2012-08-08 23:13:57          |
| 131285 |   47527 | 2012-08-08 08:33:58          |
| 131686 |   40194 | 2012-08-08 12:18:09          |
|  91749 |   11021 | 2012-08-08 12:22:05          |
+--------+---------+------------------------------+

restruct_mail_history

+----+---------+---------------------+
| id | user_id | _date               |
+----+---------+---------------------+
|  1 |   47527 | 2012-08-07 12:16:51 |
+----+---------+---------------------+

Now I need to select all user_id’s from u_contracts that have date reschedule_wait_confirm_till for tomorrow and that have no todays entires in restruct_mail_history.

So far I have a working query like this:

SELECT
  uc.user_id
FROM
  u_contracts uc
WHERE
  uc._status = 6
  AND DATE( uc.reschedule_wait_confirm_till ) = DATE( ADDDATE( now(), 1 ) )
  AND uc.user_id NOT IN ( SELECT rmh.user_id FROM restruct_mail_history rmh WHERE DATE( rmh._date ) = DATE( now() ));

Output:

19982
4622
36707
17632
40194
11021

Now I don’t like the SELECT statement in WHERE, so I was planing to make LEFT JOIN like this:

SELECT
  uc.user_id
FROM
  u_contracts uc
LEFT JOIN
  restruct_mail_history rmh
ON
  uc.user_id = rmh.user_id
WHERE
  uc._status = 6
  AND DATE( uc.reschedule_wait_confirm_till ) = DATE( ADDDATE( now(), 1 ) );

Output:

19982
4622
36707
17632
47527
40194
11021

Now this gives me all u_contracts result, but when I add the necessary parameter AND DATE( rmh._date ) != DATE( now() ) it gives me absolutelu no results.

Any idea what I’m doing wrong?

EDIT If iI change the last line to AND DATE( rmh._date ) = DATE( now() ), it gives me only the results that should not be in the list, witch id correct. Why doesn’t it work the opposite way?

Thank you already.

Answer 1

try this:

SELECT uc.user_id
FROM u_contracts uc
     LEFT JOIN restruct_mail_history rmh
        ON uc.user_id = rmh.user_id
WHERE uc._status = 6 AND
      DATE( uc.reschedule_wait_confirm_till ) = DATE( ADDDATE( now(), 1) ) AND
      (rmh.user_id IS NULL OR DATE( rmh._date ) != DATE( now() ));

see here: Visual Explanation Of Joins.