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From:SGreen Date:November 30 2005 3:48pm
Subject:Re: Rewriting subquery for old MySQL
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Alex Gemmell <agemmell@stripped> wrote on 11/30/2005 10:06:09 AM:

> Hi,
> 
> Unfortunately I need to use a query on an old MySQL (4.0.xx) and the one 

> I currently have uses a subquery.  So it works on my 4.1 but not with 
> this 4.0.  I have read in the MySQL manual that I can rewrite subqueries 

> using joins but I don't see how with this query because I only have one 
> table to check.
> 
> Basically all I'm doing is pulling out the most recent 10 activities 
> stored in a table, then reversing the order so it appears oldest first, 
> to newest (note the "$row['Assignment_ID']" is just a PHP variable):
> 
> SELECT * FROM
> (SELECT * FROM tblactivities
>   WHERE Assignment_ID=$row['Assignment_ID']
>   ORDER BY Date DESC LIMIT 10) AS tblTemp
> ORDER BY Date ASC
> 
> This works perfectly on 4.1.  How can I rewrite this to get the same 
> effect without using a subquery and so allow it to work on 4.0?
> 
> Any help gratefully recieved!
> 
> Alex
> 

To make this work on 4.0, you have to do manually something the engine did 
for you implicitly: create a temporary table.

CREATE TEMPORARY TABLE tmpSubquery SELECT * 
FROM tblactivites
WHERE Assignment_ID=$row['Assignment_ID']
  ORDER BY Date DESC LIMIT 10;

SELECT * from tmpSubquery ORDER BY Date ASC;

DROP TEMPORARY TABLE tmpSubquery;


There are only two things to remember to make this work. 
1) All of these statements must be on the same, continuously connected 
connection. You cannot close the connection between the 
statements.
2) If you do not drop the temp table and you try to execute this set of 
commands on the same continuous connection, you will get an error. 

Shawn Green
Database Administrator
Unimin Corporation - Spruce Pine
Thread
Rewriting subquery for old MySQLAlex Gemmell30 Nov
  • Re: Rewriting subquery for old MySQLSGreen30 Nov
    • Re: Rewriting subquery for old MySQLAlex Gemmell30 Nov
      • Re: Rewriting subquery for old MySQLrouvas30 Nov
        • Re: Rewriting subquery for old MySQLAlex Gemmell30 Nov
        • Re: Rewriting subquery for old MySQLAlex Gemmell30 Nov
        • Re: Rewriting subquery for old MySQLSGreen30 Nov
      • Re: Rewriting subquery for old MySQLDan Nelson30 Nov
        • Re: Rewriting subquery for old MySQLAlex Gemmell30 Nov
          • Re: Rewriting subquery for old MySQLMichael Stassen30 Nov
      • Re: Rewriting subquery for old MySQLMichael Stassen30 Nov
        • Re: Rewriting subquery for old MySQL - SOLVEDAlex Gemmell30 Nov
          • Re: Rewriting subquery for old MySQL - SOLVED - correction!Alex Gemmell6 Dec