Adding DateTime intervals with foreach loop - php

Question

I asked a question yesterday in adding together datetime intervals and was pointed to this thread - How we can add two date intervals in PHP
This is great and makes sense. However, when I try to do what the submitted answer says in a foreach loop, I'm ending up with an incorrect result.
This is a function I have made that gets all the clock in times and out times of staff, they are stored in the db and are created using PHP's date(H:i:s).
My function gets all the in and out times of any given employee, and my reporting feature I'm working on needs to display the total amount of hours they have worked.
I tried to achieve this by converting the times to datetime objects and using ->diff to get the intervals and thus calculating that days hours, I am then trying use a foreach loop to add the intervals together thus giving me a sum total of the hours worked in any given date range.
The whole function together is this:
function getTotalHours($staff_id,$from_date,$to_date){
$sql = "SELECT * FROM oc_staff_times WHERE date BETWEEN '$from_date' AND '$to_date' AND staff_id = '$staff_id'";
$result = $this->conn->query($sql);
if ($result->num_rows > 0) {
while ($row = mysqli_fetch_assoc($result)) {
$data[] = $row;
}
$base_time = new DateTime('00:00');
$total = new DateTime('00:00');
foreach ($data as $time) {
$in = new DateTime($time['clock_in_time']);
$out = new DateTime($time['clock_out_time']);
$interval = $in->diff($out);
$base_time->add($interval);
}
return $total->diff($base_time)->format("%H:%I");
}
}
I was hoping to get a monthly total, however it seems I'm only getting one days total as my final result. Here is a screen shot of the UI (the total hours are crudely circled) this also shows the time stamps my function should be adding together.

Answer 1

You can do this in a single query instead. Use TIMEDIFF() to get the difference for each row, then convert those to seconds by using TIME_TO_SEC(), SUM() those up and put it back into time-format with SEC_TO_TIME() - all in MySQL!
SELECT SEC_TO_TIME(SUM(TIME_TO_SEC(TIMEDIFF(`clock_out_time`, `clock_in_time`))))
FROM `oc_staff_times`
WHERE `staff_id` = ?
AND `date` BETWEEN ? AND ?
Making your function with a prepared statement..
function getTotalHours($staff_id, $from_date, $to_date){
$sql = "SELECT SEC_TO_TIME(SUM(TIME_TO_SEC(TIMEDIFF(`clock_out_time`, `clock_in_time`))))
FROM `oc_staff_times`
WHERE `staff_id` = ?
AND `date` BETWEEN ? AND ?";
$stmt = $this->conn->prepare($sql);
$stmt->bind_param("sss", $staff_id, $from_date, $to_date);
$stmt->execute();
$stmt->bind_result($totalTime);
$stmt->fetch();
$stmt->close();
return $totalTime;
}
SQL fiddle showing the query in action http://sqlfiddle.com/#!9/525b83/7

Answer 2

The answer from Qirel offers a nice way to do this in SQL, however if you want to understand why your code didn't work:
$base_time = new DateTime('00:00'); does not create an interval, it's a date. It means that if you add 24 hours to it and ask only the time part, it will show '00:00' because you end up the day after.
One solution would have been to declare $base_time as an interval, for example like this:
$base_time = new DateInterval('PT0S');
And at the end output directly like this:
$base_time->format("%H:%I");