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-   -   Can't get MySQL JOINs to work right (https://vborg.vbsupport.ru/showthread.php?t=137015)

thincom2000 01-20-2007 08:42 AM
Can't get MySQL JOINs to work right
 
I am trying to write a single query that does the following:

- reads all threads where forumid = $forumid
- reads all posts where threads.firstpostid = postid
- reads all polls where threads.pollid = pollid, but only if a poll exists

I tried:

PHP Code:
SELECT thread.*, post.*, IF(thread.pollid = poll.pollid, poll.*, '')
FROM " . TABLE_PREFIX . "thread, " . TABLE_PREFIX . "post, " . TABLE_PREFIX . "poll"
WHERE thread.forumid = '" . $forumid . "'
    AND post.postid = thread.firstpostid
    AND IF(thread.pollid = poll.pollid, poll.pollid = thread.pollid, '1 > 0')
ORDER BY dateline DESC 
but it just gives T_STRING errors and returns NULL...

Marco van Herwaarden 01-20-2007 08:58 AM
Use LEFT JOIN's.

thincom2000 01-20-2007 04:13 PM
I don't think this has the same meaning as what I suggested in my first post, but here it is with LEFT JOINs and still not working (database error):

Code:
SELECT thread.*, post.*, IF(thread.pollid = poll.pollid, 'poll.*', '')
FROM " . TABLE_PREFIX . "thread AS thread
LEFT JOIN " . TABLE_PREFIX . "post AS post ON (post.postid = thread.firstpostid)
IF(thread.pollid = poll.pollid, 'LEFT JOIN " . TABLE_PREFIX . "poll AS poll ON (poll.pollid = thread.pollid)', '')
WHERE thread.forumid = " . $forumid . "

ConqSoft 01-20-2007 04:31 PM
What's the error given?

thincom2000 01-20-2007 04:35 PM
Code:
SQL query:

SELECT thread. * , post. * , IF( thread.pollid = poll.pollid, 'poll.*', '' )
FROM forum_thread AS thread
LEFT JOIN forum_post AS post ON ( post.postid = thread.firstpostid ) IF( thread.pollid = poll.pollid, 'LEFT JOIN forum_poll AS poll ON (poll.pollid = thread.pollid)', '' )
WHERE thread.forumid =2
LIMIT 0 , 30

MySQL said:
#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'IF( thread . pollid = poll . pollid , 'LEFT JOIN forum_poll AS poll ON (poll.pol' at line 1
Removed the entire poll table check from the query. All I need is to check if a poll exists anyway, which can be done with thread.pollid

Was returning NULL because I somehow deleted every record in my post table. Good thing I made a backup yesterday.

Now the query works as expected:

Code:
SELECT thread.*, post.*
FROM " . TABLE_PREFIX . "thread AS thread
LEFT JOIN " . TABLE_PREFIX . "post AS post ON (post.postid = thread.firstpostid)
WHERE thread.forumid = " . $forumid . "


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