Hi,
Won't it be possible the MySQL parser optimize the SELECT y FROM x ORDER BY
z DESC LIMIT 1 as :
SELECT MAX(z) FROM x;
followed by :
SELECT y FROM x WHERE z=a;
(where 'a' is the result of the first SELECT MAX(z) query)
The speed gain is quite apreciable when there is a lot of rows :
(# Time: 010905 22:14:00
# User@Host: mysql[mysql] @ localhost []
# Time: 9 Lock_time: 0 Rows_sent: 1 Rows_examined: 7718
SELECT contenu,pseudo,signature FROM threadhardwarefr7 WHERE numeropost=5347
ORDER BY numreponse DESC LIMIT 1;)
mysql> SELECT contenu,pseudo,signature FROM threadhardwarefr7 WHERE
numeropost=5347 ORDER BY numreponse DESC LIMIT 1;
+------------------------------------------+-------------+-----------+
| contenu | pseudo | signature |
+------------------------------------------+-------------+-----------+
| umff > :hello:
meme kestion que sad | Biff Tannen | 1 |
+------------------------------------------+-------------+-----------+
1 row in set (8.29 sec)
mysql> SELECT MAX(numreponse) FROM threadhardwarefr7 WHERE numeropost=5347;
+-----------------+
| MAX(numreponse) |
+-----------------+
| 1032001 |
+-----------------+
1 row in set (0.00 sec)
mysql> SELECT contenu,pseudo,signature FROM threadhardwarefr7 WHERE
numreponse=1032001;
+------------------------------------------+-------------+-----------+
| contenu | pseudo | signature |
+------------------------------------------+-------------+-----------+
| umff > :hello:
meme kestion que sad | Biff Tannen | 1 |
+------------------------------------------+-------------+-----------+
1 row in set (0.00 sec)
What do you think about this ?
Jocelyn Fournier
Presence-PC
