Question

This is my scenario: I have a table that contains events, every event has a field called ‘created’ with the timestamp in which that event was created. Now I need to sort the events from newest to oldest, but I do not want MySQL to return them all. I need only the latest in a given interval, for example in a range of 24 hours (EDIT: I’d like to have a flexible solution, not only for a 24 hours range, but maybe every few hours). And I only need for the last 10 days. I have achieved that but i’m sure in the most inefficient ways possible, that is, something like that:

$timestamp = time();

for($i = 0; $i < 10; $i++) {
    $query = "SELECT * FROM `eventos` WHERE ... AND `created` < '{$timestamp}' ORDER BY `created` DESC LIMIT 1";    
    $return = $database->query( $query );

    if($database->num( $return ) > 0) {
        $event = $database->fetch( $return );
        $events[] = $event;

        $timestamp = $timestamp - 86400;
    }
}

I hope I was clear enough. Thanks,
Jesús.

Answer 1

Assuming you want the latest (having the greatest created date) event per day for the last 10 days.

so let’s get the latest timestamp per day

$today = date('Y-m-d');
$tenDaysAgo = date('Y-m-d', strtotime('-10 day'));

$innerSql = "SELECT date_format(created, '%Y-%m-%d') day, MAX(created) max_created FROM eventos WHERE date_format(created, '%Y-%m-%d') BETWEEN '$today' and '$tenDaysAgo' GROUP BY date_format(created, '%Y-%m-%d')";

Then we can select all the events that match those created dates

$outerSql = "SELECT * FROM eventos INNER JOIN ($innerSql) as A WHERE eventos.created = A.max_created";

I haven’t had a chance to test this, but the principles should be sound enough.

If you want to group by some other arbitrary number of hours you would change innerSql:

$fromDate = '2012-07-06' // or if you want a specific time '2012-07-06 12:00:00'
$intervalInHours = 5;
$numberOfIntervals = 10;

$innerSql = "SELECT FLOOR(TIMESTAMPDIFF(HOUR, created, '$fromDate') / $intervalInHours) as grouping, MAX(created) as max_created FROM eventos WHERE created BETWEEN DATE_SUB('$fromDate', INTERVAL ($intervalInHours * $numberOfIntervals) HOUR) AND '$fromDate' GROUP BY FLOOR(TIMESTAMPDIFF(HOUR, created, '$fromDate') / $intervalInHours)";