Question

Assuming I have table called events with the columns

INT  id
DATETIME start_time
DATETIME end_time

how would I find all rows where any part of the time range from start_time to end_time falls within a certain hour range?

For example, I may want to find rows where the events had some portion of them during the 8-10pm hour range.

Something like

select * from events where (hour(start_time) IN (20, 21, 22)) or (hour(end_time) IN (20, 21, 22))

would work, except for events that started before 8pm and ended after 11pm.

Lastly, it has to work across day boundaries, so a range like 23-2 (11pm – 2am) should also work.

Unfortunately I’m unable to modify the schema of the table.

Answer 1

I managed to make this work with the day boundaries requirement. It’s ugly, but it seems to cover all the cases.

While you could write a stored procedure to do it, it’s easier to express in Java, so:

public void checkEvents (int[][] events, int startHour, int endHour)    

  final int START         = 0;
  final int END           = 1;
  final int HOURS_PER_DAY = 24;

  for (int[] event : events) {

    int start = startHour;
    int end = (endHour < startHour) ? endHour + HOURS_PER_DAY : endHour;

    int eventStart = event[START];
    int eventEnd = (event[END] < event[START]) ? event[END] + HOURS_PER_DAY : event[END];

    if (checkOverlap(result, event, start, end, eventStart, eventEnd))
    || (checkOverlap(result, event, start, end, eventStart + HOURS_PER_DAY, eventEnd + HOURS_PER_DAY))
      || (checkOverlap(result, event, start + HOURS_PER_DAY, end + HOURS_PER_DAY, eventStart, eventEnd))
       || (!checkOverlap(result, event, start + HOURS_PER_DAY, end + HOURS_PER_DAY, eventStart + HOURS_PER_DAY, eventEnd + HOURS_PER_DAY);
          System.out.println("overlapped!");
  }
}

private boolean checkOverlap(ArrayList<int[]> result, int[] event, int start, int end, int eventStart, int eventEnd) {

  if ((eventStart >= start && eventStart < end) || (eventStart < start && eventEnd > start)) {
    return true;
  }

  return false;
}