Display latest temperature by location quickly - php

Question

The Table I have has temperatures, locations and datetime and other data that isn't currently used. Message is the temperature and locationmap is where the sensor is ie, lounge, kitchen, outside!)
Query :
SELECT
t1.*
FROM
temperatures t1
JOIN (
SELECT
locationmap
, MAX(timeof) AS timeof
FROM
temperatures
GROUP BY
locationmap
) AS t2
ON t1.locationmap = t2.locationmap AND t1.timeof = t2.timeof
WHERE
DATE(t1.timeof) BETWEEN DATE_SUB(CURDATE(), INTERVAL 5 MINUTE) AND CURDATE()";
Resulting PHP code to display current temperatures;
// Print out result
while($row = mysql_fetch_array($result)){
echo $row['locationmap']. " - ". $row['message']. " #". $row['timeof'];
echo "<br />";
}
Just want it to display the latest temperature for each location, which it currently does, but I was wondering if this the best optimised query for speed, as at the moment it takes 7secs to display results!? Mind u I have a slow server, but I'm the only user.
Thx.
FYI.

Answer 1

Can't say without table create statements, more information about indexes and storage engine
And please make your SQL code more readable in your PHP code, It's damn hard to read like this.
SELECT
t1.*
FROM
temperatures t1
JOIN (
SELECT
locationmap
, MAX(timeof) AS timeof
FROM
temperatures
GROUP BY
locationmap
) AS t2
ON t1.locationmap = t2.locationmap AND t1.timeof = t2.timeof
WHERE
DATE(t1.timeof) BETWEEN DATE_SUB(CURDATE(), INTERVAL 5 MINUTE) AND CURDATE()
The same query but more readable
And thanks for the minus 1, because i tryed to help...
This query should run sightly faster
SELECT
t1.locationmap
, t1.message
, t1.timeof
FROM
temperatures AS t1
JOIN (
SELECT
locationmap
, MAX(timeof) AS timeof
FROM
temperatures
GROUP BY
locationmap
) AS t2
ON t1.locationmap = t2.locationmap AND t1.timeof = t2.timeof
WHERE
DATE(t1.timeof) BETWEEN DATE_SUB(CURDATE(), INTERVAL 5 MINUTE) AND CURDATE()
And make sure you have a covering BTREE (if you use MyISAM or innodb indexes are already BTREE) index on locationmap, timeof and message (optional) (be sure you build the index like this)
Please note that inserts, updates and deleted run sightly slower because of the covering index.
So try to multiinsert to keep the speed up.