Question

In my model I have the following query which average $probe values hour by our for the last day available in the database.

$connection=Yii::app()->db;
$command=$connection->createCommand("SELECT AVG($probe), TIME FROM tbl_sensors GROUP BY DATE(TIME), HOUR(TIME) ORDER BY ID DESC LIMIT 0, 24");
$dataReader=$command->query();

Now I’d like to modify this query to get the result for yesterday, the day before yesterday etc.

My first thought was to add a variable fed by the controller modify LIMIT parameters. Though the following:

SELECT AVG($probe), TIME FROM tbl_sensors GROUP BY DATE(TIME), HOUR(TIME) ORDER BY ID DESC LIMIT 24, 48

returns 48 values instead of 24. I don’t understand why is that?

Any pointers welcome

Answer 1

LIMIT 24, 48 doesn’t mean from 24 to 48. it means from 24 to (24+48).
if I say in another way, it starts from 24, get 48 records .

LIMIT 24, 24

http://dev.mysql.com/doc/refman/5.1/en/select.html

but I recommend you to use WHERE

SELECT AVG($probe), TIME FROM tbl_sensors
WHERE `TIME` BETWEEN ... AND ...
GROUP BY DATE(TIME), HOUR(TIME)
ORDER BY ID DESC LIMIT 0, 24