Skip navigation links

MySQL Forums :: Performance :: Join Order and performance


Advanced Search

Re: Join Order and performance
Posted by: scott cornwell ()
Date: March 29, 2006 03:16PM

I spent the day playing with this and I turned on the log_slow_queries - one thing i did discover for the following when these tables are large is the order does matter (using mysql 4.1)

Examining the slow_log, Switching the order makes a HUGE difference where the first example shows that maybe 1654032 rows are examined in 122 seconds - switching this then shows that only 434211 rows were examined in like 8 seconds


> for example would
> SELECT T1.*, T2.*, T3.* FROM T1
> LEFT JOIN T2 ON T1.id = T2.id
> LEFT JOIN T3 ON T1.id = T3.id
> WHERE ......
>
> be any major difference than the following (T3 is
> joined on first)
> SELECT T1.*, T2.*, T3.* FROM T1
> LEFT JOIN T3 ON T1.id = T3.id
> LEFT JOIN T2 ON T1.id = T2.id
> WHERE ......

Options: ReplyQuote


Subject Views Written By Posted
Join Order and performance 7526 scott cornwell 03/28/2006 12:37PM
Re: Join Order and performance 3320 03/28/2006 03:14PM
Re: Join Order and performance 2094 scott cornwell 03/29/2006 03:16PM
Re: Join Order and performance 1732 03/29/2006 03:26PM


Sorry, you can't reply to this topic. It has been closed.

Content reproduced on this site is the property of the respective copyright holders. It is not reviewed in advance by Oracle and does not necessarily represent the opinion of Oracle or any other party.