SQL Query - Pull User Achievement - sql

Question

First, I am sorry as I could not come up with better title for this question.
I have a badge/achievement system in my website, community users are rewarded specific badges according to their activity in the website, below sql example I use to pull the number of users who made at at least 100 forum posts (I am using informix db version 10)
SELECT tjm.userid::INTEGER AS user_id,
EXTEND(DBINFO("UTC_TO_DATETIME",tjm.creationdate/1000), year to fraction)
AS earned_date
FROM TABLE(
MULTISET(
SELECT jm.userid, jm.creationdate, (
SELECT COUNT(*) from TABLE(
MULTISET(
SELECT userid, creationdate
FROM jive:jivemessage
)
) AS i
WHERE i.userid = jm.userid AND i.creationdate < jm.creationdate
) + 1 AS row_num
FROM jive:jivemessage jm
)
) AS tjm
WHERE tjm.row_num=100
This sql takes around more than 30 minutes to execute, we have a very large community and there are millions of forum posts.
I would like to know if there is a solution to improve the query performance? I am trying to reduce the execution time because I have 40 sql queries similar to this one but for different tables and activities.

Answer 1

I don't now Informix DB, but the query below should do what you ask and it's ANSI SQL (except for the EXTEND part, which I copied from your original query).
SELECT
jm.userid
,EXTEND(DBINFO("UTC_TO_DATETIME",tjm.creationdate/1000), year to fraction) AS earned_date
FROM
(
-- This sub-query will return all Users who have 100 messages or more
SELECT
jm.userid
,count(jm.userid) as totalmessages
FROM
jive:jivemessage jm
GROUP BY
jm.userid
HAVING
count(jm.userid) >= 100) AS MessageCount
The above could probably be done without having to use a sub-query. The only reason why I used it is to have the DateEarned, as per original query, in the result set. Adding it to the sub-query would have required adding it to the GROUP BY, with unpredictable results if the query runs across two days (e.g. at 23:59:59).
Update 2012/08/14 - Rewritten query following new requirements
As I stated before, I don't know Informix at all, therefore the following query may or may not run.
SELECT
UsersWithBadge.userid
,MAX(UsersWithBadge.creationdate) as dateearned
FROM
(
SELECT FIRST 100
jm.userid
,jm.creationdate
FROM
jive:jivemessage jm
JOIN
(-- This sub-query will return all Users who have 100 messages or more
SELECT
jm.userid
,count(jm.userid) as totalmessages
FROM
jive:jivemessage jm
GROUP BY
jm.userid
HAVING
count(jm.userid) >= 100)
AS MessageCount ON
(MessageCount.userid = jm.userid)
) AS UsersWithBadge
GROUP BY
UsersWithBadge.userid