How to add column value to SQL LIKE query?

Question

I'm trying to perform the following query using MySQL:

SELECT e.event, 
       BINARY e.params as params, 
       UNIX_TIMESTAMP(e.datetime) AS datetime, 
       p.postid AS postid,
       q.postid AS parentid 
FROM qa_eventlog as e 
         LEFT JOIN qa_posts as p 
         LEFT JOIN qa_posts as q ON e.userid=1 AND 
              DATE_SUB(CURDATE(),INTERVAL 30 DAY) <= datetime AND 
              e.params LIKE '%postid='+p.postid+'%' AND 
              e.params LIKE '%parentid='+q.postid+'%' 
ORDER BY datetime DESC

but it gives the following error:

Error 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 '+p.postid+'%' AND e.params LIKE '%parentid='+q.postid+'%' ORDER BY datetime DESC' at line 1

It seems it doesn't like the + sign, which I thought was the correct way to add values in a query; guess not :) How do I ask it to check if the column value of one table (an integer) is in the column value of another table (a string)?

Edit: Thanks for the answers, here's the code that worked, using CONCAT :

SELECT e.event, 
    BINARY e.params as params, 
    UNIX_TIMESTAMP(e.datetime) AS datetime,
    p.postid AS postid, 
    q.postid AS parentid 
FROM qa_eventlog AS e 
    LEFT JOIN qa_posts AS p 
        ON e.params LIKE CONCAT('%postid=', p.postid, '%' ) 
    LEFT JOIN qa_posts AS q 
        ON e.params LIKE CONCAT('%postid=', q.postid, '%' ) 
WHERE e.userid=1 
    AND DATE_SUB(CURDATE(),INTERVAL 30 DAY) <= datetime 
ORDER BY datetime DESC

Answer 1

try this one,

SELECT e.event, 
       e.params as params, 
       UNIX_TIMESTAMP(e.datetime) AS datetime, 
       p.postid AS postid,
       q.postid AS parentid 
FROM qa_eventlog as e 
         LEFT JOIN qa_posts as p 
             ON e.id = p.id        -- not sure on this. please supply
                                   -- the correct linking columnID
         LEFT JOIN qa_posts as q 
             ON e.id = q.id        -- and this
WHERE  (DATE_SUB(CURDATE(),INTERVAL 30 DAY) <= datetime) AND 
       e.params LIKE CONCAT('%', 'postid=', p.postid, '%' )  AND 
       e.params LIKE CONCAT('%', 'parentid=', q.postid, '%' )  AND
       e.userid = 1
ORDER BY datetime DESC

Answer 2

See the MySQL docs for CONCAT() : http://dev.mysql.com/doc/refman/5.1/en/string-functions.html#function_concat

Such like:

SELECT e.event, 
       BINARY e.params as params, 
       UNIX_TIMESTAMP(e.datetime) AS datetime, 
       p.postid AS postid,
       q.postid AS parentid 
FROM qa_eventlog as e 
         LEFT JOIN qa_posts as p 
         LEFT JOIN qa_posts as q ON e.userid=1 AND 
              DATE_SUB(CURDATE(),INTERVAL 30 DAY) <= datetime AND 
              e.params LIKE CONCAT('%postid=',p.postid,'%') AND 
              e.params LIKE CONCAT('%parentid=',q.postid,'%')
ORDER BY datetime DESC