PHP - Grouping Duration based events / rows into single html blocks - php

Question

So I've got a bunch of 'events' in a table in which they have a start and an end column (both DATETIME). I'm fetching every event for a single day and somehow need to group them together so that they can be displayed as a single HTML block.
For example...
Row #1: Has a duration of 30 minutes, starts at 09:00:00 and ends at 09:30:00
Row #2: Has a duration of 30 minutes, starts at 09:30:00 and ends at 10:00:00
Row #3: Has a duration of 90 minutes, starts at 12:00:00 and ends at 13:30:00
What would be the best way to know that I need 2 html blocks... One that is a div that has a 60px height (for rows 1 and 2), and then because there's a break between 10:00:00 and 12:00:00 to have the another div that is 90px height (row 3).
Can this be done with MySQL somehow? Or do I have to do a PHP loop to check for empty spaces of time in order to know when I should close a div and begin a new one?
Any help would be beneficial.
This is more of a logic question than code question.

Answer 1

You can do this in MySQL. One way is using a correlated subquery to determine when "event periods" begin. A new event period begins when it does not overlap with any others. Then use this information to assign an "event period id" to each event.
Such a query would perform reasonably well with the right indexes.
You could do this in php. I am biased toward putting such logic into the database rather than in application code.

Answer 2

My personal bias is to keep formatting out of the database layer. I would do this using PHP.
Assumptions based on the text of your question:
Duration is stored in the database
Duration increment = 30 minutes
Events do not overlap.
Duration data has been queried with ODBC
Duration query includes ORDER BY Start_Time
Duration data loaded into appropriate $result variables
Event blocks are 30px per event.
$job_count = 0;
$event_increment = 30;
$event_height = 30;
$this_block_height = 0;
$this_block_content = "";
while(odbc_fetch_row($result)) {
//fetch all your results into arrays
$duration[] = odbc_result($result, 1);
$start_time[] = odbc_result($result, 2);
$end_time[] = odbc_result($result,3);
$event_count++;
}
for($x=0;$x < $event_count; $x++) {
//loop through the arrays to format the blocks
if($x + 1 == $job_count) {
//if this is true, we are at the last element
$this_block_height += $event_height;
$this_block_content .= $start_time[$x] . " to " . $end_time[$x] . PHP_EOL;
echo "<DIV style='height:" . $this_block_height . "px;'>$this_block_content</DIV>";
}
else {
if($end_time[$x] == $start_time[$x+1]) {
//if this is true there is no gap.
$this_block_height += $event_height;
$this_block_content .= $start_time[$x] . " to " . $end_time[$x] . PHP_EOL;
}
else {
//gap identified
//write old block to file with padding on the end
//reset values to start over
$end_seconds = strtotime($end_time[$x]);
$start_seconds = strtotime($start_time[$x+1]);
$gap = $start_seconds - $end_seconds;
$gap_minutes = $gap / 3600;
$gap_increments = $gap_minutes / $event_increment;
$this_block_height += ($event_height * $gap_increments);
echo "<DIV style='height:" . $this_block_height . "px;'>$this_block_content</DIV>";
//this will put the space padding at the end of the first block
//instead of at the start of the second block
$this_block_height = 0;
$this_block_content = "";
}
}
}