"Jeff Oien" <[EMAIL PROTECTED]> wrote in message
[EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
> I'm having a hard time learning how to get an average. I have a database
> that gets a number and inserts in into a MySQL database every 1/2 hour
> during the day. For the current half hour, I want to get the last 15 days
> numbers for the same time as the time it is now. I can retrieve and
display
> the numbers fine, I just don't know how to go about putting these all into
> variables or an array or if I can do this within a query and then take an
> average for them.
First, a modified 'do-it-in-PHP' solution to return
the average of an arbitrary number of results:
<?php
$result = mysql_query($query);
$num = mysql_num_rows($result);
$sum = 0;
while ($row = mysql_fetch_array($result))
$sum += $row["val"];
$avg = $sum/$num;
?>
And two variants on 'do-it-in-SQL-
and-just-get-the-answer':
SELECT AVG(val)
FROM table
WHERE halfhour = $nowAsHalfHour
ORDER BY date DESC
LIMIT 15
or, alternatively,
SELECT AVG(val)
FROM table
WHERE halfhour = $nowAsHalfHour
AND date > $nowMinus15Days
;-)
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