Hey all, I've read the pages in the MySQL manual that explain the types of JOINs many times, but still think I'm missing something.
I usually was always using INNER JOIN in all my join queries, and in a few cases LEFT JOIN (in cases I wanted the rows in one table that were not in the other one). I've started to discover, with the help of EXPLAIN, that the join type can seriously affect performance. For example, I had a query such as this: SELECT a.field FROM table1 a INNER JOIN table2 b USING (field2) ORDER BY b.field3 DESC It was using both filesort and a temporary table (in EXPLAIN) and took about 4.50 seconds to run. I switched the order of the tables in the join, putting table2 first, and nothing changed in my EXPLAIN. I then changed the join to LEFT JOIN, and suddenly I had no more filesort or temporary table, and the query took 0.05 seconds ! I compared that I got the same rows in my result both ways, and indeed I did. I'm positive I can improve many of my queries this way, but feel I need to understand the JOINs better. If someone can point me to a guide on this someplace, other than the mysql manual (as Ive already read it few times but it didnt explain their differences and uses very well), I'd greatly appreciate it =) Or, if you simply want to give the explanation yourself, that's fine too. Thanks, -- Keith Bussey Mana Internet Solutions, Inc. Chief Technology Manager +50 6 280 2284 ext.108 -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED]
