Question

I’m trying to query mysql for an average of SUM time (taken from datetime fields) for multiple records in order to get an output like: 22:38

My datetime field checkin_time contains data like:

2012-03-16 22:48:00 // the time here: 22:48 is what's interesting to me
2012-03-16 02:28:32
2012-03-16 00:28:47
0000-00-00 00:00:00

My plan was to extract and select the sum time from all datetime fields, then converting the sum to unix timestamp, divide the sum by total number of records and finally convert it back to time his format. This (see code below) however gives me nothing, no error no nothing. I also realized empty fields like: 0000-00-00 00:00:00 were not to be taken into account to produced relevant data.

Can anyone please help me pointing out the mistakes or perhaps explain the theory behind how you would do it? This is what i got so far:

Edit: Thanks to Damiqib for suggesting a working SQL query, still not entirely correct though. The code below outputs 01:00 when it should be 23:15 something.

 $getCheckinTime = mysql_query("SELECT COUNT(id), SEC_TO_TIME( AVG( TIME_TO_SEC(  `checkin_time` ) ) ) AS averageTime FROM guests WHERE checkin_time != '0000-00-00 00:00:00'") or die(mysql_error());
while($checkIn = mysql_fetch_array($getCheckinTime)) { 

    $timestamp = strtotime($checkIn['averageTime']);
    $UnixTimeStamp = date("Y-m-d H:i:s", $timestamp); //converting to unix
    $avgUnix = $UnixTimeStamp / $checkIn['COUNT(id)']; // calculating average
    $avgTime = date('H:i', $avgUnix); // convert back to time his format
    echo $avgTime; //outputs 01:00, got to be incorrect should be 23:15 something

}

Thanks in advance

Edit: Solution (thanks to Damiqib):

$avgCheckinTime = array();
$getCheckinTime = mysql_query("SELECT TIME(`checkin_time`) AS averageTime    FROM guests    WHERE checkin_time !=  '0000-00-00 00:00:00'") or die(mysql_error());
while($checkIn = mysql_fetch_array($getCheckinTime)) { 

    array_push($avgCheckinTime, $checkIn['averageTime']);
}

// = array('22:00:00', '22:30:00'...)
    $times = $avgCheckinTime;

    $fromReplace = array('22' => '00',
                   '23' => '01',
                   '00' => '02',
                   '01' => '03',
                   '02' => '04',
                   '03' => '05',
                   '04' => '06',
                   '05' => '07');

  $timeSum = 0;

  //Iterate through all given times and convert them to seconds
  foreach ($times as $time) {
   if (preg_match ('#^(?<hours>[\d]{2}):(?<mins>[\d]{2}):(?<secs>[\d]{2})$#',$time, $parse)) {
  $timeSum += (int) $fromReplace[$parse['hours']] * 3600 + (int) $parse['mins'] * 60 + (int) $parse['secs'] . '<br />';

  //echo $time . ' ' . ($fromReplace[$parse['hours']] *3600) .  '<br />'; 
  }
}

   $toReplace = array('00' => '22',
                 '01' => '23',
                 '02' => '00',
                 '03' => '01',
                 '04' => '02',
                 '05' => '03',
                 '06' => '04',
                 '07' => '05');

 $time = explode(':', gmdate("H:i:s", $timeSum / count($times)));

 $averageCheckinTime = $toReplace[$time[0]] . ':' . $time[1] . ':' . $time[2];

 //This is the final average time biased between 22-05
 echo $averageCheckinTime;

Answer 1

This seemed to work with my test data:

SELECT SEC_TO_TIME(AVG(TIME_TO_SEC(`time`))) AS averageTime
FROM guests 
WHERE checkin_time != '0000-00-00 00:00:00'

UPDATE:

-- Table structure for table `guests`
CREATE TABLE `guests` (
  `checkin_time` datetime NOT NULL,
  KEY `checkin_time` (`checkin_time`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;

-- Dumping data for table `guests`
INSERT INTO `guests` VALUES('2012-08-17 17:30:00');
INSERT INTO `guests` VALUES('2012-08-17 18:30:00');
INSERT INTO `guests` VALUES('2012-08-17 19:30:00');
INSERT INTO `guests` VALUES('2012-08-17 20:30:00');
INSERT INTO `guests` VALUES('2012-08-17 21:30:00');


Showing rows 0 - 0 (1 total, Query took 0.0003 sec)
SELECT SEC_TO_TIME( AVG( TIME_TO_SEC(  `checkin_time` ) ) ) AS averageTime
FROM guests
WHERE checkin_time !=  '0000-00-00 00:00:00'
LIMIT 0 , 30

Result

averageTime
19:30:00

At least with my test data this seems to be working?

ANOTHER UPDATE

<?php

  /*
    SELECT TIME(`checkin_time`) AS averageTime
    FROM guests
    WHERE checkin_time !=  '0000-00-00 00:00:00'
  */

  // = array('22:00:00', '22:30:00'...)
  $times = RESULT_FROM_QUERY_AS_AN_ARRAY_OF_TIMES;

  $fromReplace = array('22' => '00',
                       '23' => '01',
                       '00' => '02',
                       '01' => '03',
                       '02' => '04',
                       '03' => '05',
                       '04' => '06',
                       '05' => '07');

  $timeSum = 0;

  //Iterate through all given times and convert them to seconds
  foreach ($times as $time) {
    if (preg_match ('#^(?<hours>[\d]{2}):(?<mins>[\d]{2}):(?<secs>[\d]{2})$#',$time, $parse)) {
      $timeSum += (int) $fromReplace[$parse['hours']] * 3600 + (int) $parse['mins'] * 60 + (int) $parse['secs'] . '<br />';

      echo $time . ' ' . ($fromReplace[$parse['hours']] *3600) .  '<br />'; 
    }
  }

  $toReplace = array('00' => '22',
                     '01' => '23',
                     '02' => '00',
                     '03' => '01',
                     '04' => '02',
                     '05' => '03',
                     '06' => '04',
                     '07' => '05');

  $time = explode(':', gmdate("H:i:s", $timeSum / count($times)));

  $averageCheckinTime = $toReplace[$time[0]] . ':' . $time[1] . ':' . $time[2];

  //This is the final average time biased between 22-05
  echo $averageCheckinTime;   

?>