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php – Check if two times overlap

Posted by: admin July 12, 2020 Leave a comment

Questions:

I want to see if a time I read from a db overlaps with a time provided by a user.

My database looks like this:

-----------------------------------------------
|organiser|meeting_start|meeting_end|boardroom|
-----------------------------------------------
| John Doe| 1340193600  | 1340195400| big     |
-----------------------------------------------

My code looks like this:

date_default_timezone_set('Africa/Johannesburg');
$from = strtotime($_GET['meeting_date'] . ' ' . $_GET['meeting_start']);
$to = strtotime($_GET['meeting_date'] . ' ' . $_GET['meeting_end']);
$another_meeting = false;
$meeting_date = strtotime($_GET['meeting_date']);
$meeting_next = $meeting_date + 86400;

$result = mysql_query("SELECT meeting_start, meeting_end FROM admin_boardroom_booking WHERE boardroom = '" . $_GET['boardroom'] . "' AND meeting_start >= '" . $meeting_date . "' AND meeting_end < '" . $meeting_next . "'")or die(mysql_error());
while($row = mysql_fetch_array($result)) {
    $from_compare = $row['meeting_start'];
    $to_compare = $row['meeting_end'];

    $intersect = min($to, $to_compare) - max($from, $from_compare);
    if ( $intersect < 0 )
        $intersect = 0;

    $overlap = $intersect / 3600;
    if ( $overlap <= 0 ) {
        $another_meeting = true;
        break;
    }
}

if ($another_meeting)
    echo 'ERROR';

If I type two overlapping times on purpose, it doesn’t echo error. What am I doing wrong?

How to&Answers:

Two time periods P1 and P2 overlaps if, and only if, at least one of these conditions hold:

  1. P1 starts between the start and end of P2 (P2.from <= P1.from <= P2.to)
  2. P2 starts between the start and end of P1 (P1.from <= P2.from <= P1.to)

This will catch partly overlapping periods as well as periods where one completely covers the other. One of the periods must always start (or end) inside the other if they are overlapping.

So $another_meeting would be defined by:

$another_meeting = ($from >= $from_compare && $from <= $to_compare) ||
                   ($from_compare >= $from && $from_compare <= $to);

You may want to change the borderline cases to strict < checks if one event can start at the exact same time as another ends.

Answer:

Was just doing something similar…. but just with times….

$startTime = strtotime("7:00");
$endTime   = strtotime("10:30");

$chkStartTime = strtotime("10:00");
$chkEndTime   = strtotime("12:10");

if($chkStartTime > $startTime && $chkEndTime < $endTime)
{
    // Check time is in between start and end time
    echo "1 Time is in between start and end time";
}
elseif(($chkStartTime > $startTime && $chkStartTime < $endTime) || ($chkEndTime > $startTime && $chkEndTime < $endTime))
{
    // Check start or end time is in between start and end time
    echo "2 ChK start or end Time is in between start and end time";
}
elseif($chkStartTime==$startTime || $chkEndTime==$endTime)
{
    // Check start or end time is at the border of start and end time
    echo "3 ChK start or end Time is at the border of start and end time";
}
elseif($startTime > $chkStartTime && $endTime < $chkEndTime)
{
    // start and end time is in between  the check start and end time.
    echo "4 start and end Time is overlapping  chk start and end time";
}

Answer:

I’d probably solve it with something like this:

function avaliable($start, $end) {
  // checks if there's a meeting between start or end
  $q = "SELECT * FROM admin_boardroom_booking "
    . "WHERE NOT (meeting_start BETWEEN '$end' AND '$start' "
    . "OR meeting_end BETWEEN '$end' AND '$start')";
  $result = mysql_query($q);

  // returns true on no conflicts and false elseway
  return mysql_num_rows($result) === 0;
}

Answer:

Emil Vikström’s answer is correct, but there is a scenario needed to be considered.
Like, One of the time ranges is a subset of another time range.
So, assume that P1{start_time, end_time} and P2{start_time, end_time} will overlap when any of the following is true.

  • P1.start_time <= P2.start_time <= P1.end_time
  • P1.start_time <= P2.end_time <= P1.end_time
  • P2.start_time <= P1.start_time <= P1.end_time <= P2.end_time

Just assuming that the times are sorted in ascending order. Example below:

|-----------------------------------|
|  Start time  |   End time  | Name |
|-----------------------------------|
|    10:00     |    14:00    |  P1  |
|-----------------------------------|
|    12:00     |    16:00    |  P2  |
|-----------------------------------|
|    08:00     |    12:00    |  P3  |
|-----------------------------------|
|    07:00     |    16:00    |  P4  |
|-----------------------------------|

If you consider P1 as the base time and you want to check P2, P3, P4 against it.

  1. P1.start_time <= P2.start_time <= P1.end_time true
  2. P1.start_time <= P3.end_time <= P1.end_time true
  3. P4.start_time <= P1.start_time <= P1.end_time <= P4.end_time true

This is how you can check if any of the time is overlapping another one or not.

Answer:

In case when $to is always later than $from we can use this more shorter solutions

$another_meeting = !($from > $to_compare || $from_compare > $to);