PHP and MySQL - efficiently handling multiple one to many relationships

Question

I am seeking some advice on the best way to retrieve and display my data using MySQL and PHP.

I have 3 tables, all 1 to many relationships as follows:

Each SCHEDULE has many OVERRIDES and each override has many LOCATIONS. I would like to retrieve this data so that it can all be displayed on a single PHP page e.g. list out my SCHEDULES. Within each schedule list the OVERRIDES, and within each override list the LOCATIONS.

Option1 - Is the best way to do this make 3 separate SQL queries and then write these to a PHP object? I could then iterate through each array and check for a match on the parent array.

Option 2 - I have thought quite a bit about joins however doing two right joins will return me a row for every entrance in all 3 tables.

Any thoughts and comments would be appreciated.

Best regards, Ben.

Answer 1

If you really want every piece of data, you're going to be retrieving the same number of rows, no matter how you do it. Best to get it all in one query.

SELECT schedule.id, overrides.id, locations.id, locations.name
FROM schedule
JOIN overrides ON overrides.schedule_id = schedule.id
JOIN locations ON locations.override_id = overrides.id
ORDER BY schedule.id, overrides.id, locations.id

By ordering the results like this, you can iterate through the result set and move on to the next schedule whenever the scheduleid changes, and the next location when the locationid changes.

Edit: a possible example of how to turn this data into a 3-dimensional array -

$last_schedule = 0;
$last_override = 0;
$schedules = array();

while ($row = mysql_fetch_array($query_result))
{
  $schedule_id = $row[0];
  $override_id = $row[1];
  $location_id = $row[2];
  $location_name = $row[3];
  if ($schedule_id != $last_schedule)
  {
    $schedules[$schedule_id] = array();
  }
  if ($override_id != $last_override)
  {
    $schedules[$schedule_id][$override_id] = array();
  }
  $schedules[$schedule_id][$override_id][$location_id] = $location_name;
  $last_schedule = $schedule_id;
  $last_override = $override_id;
}

Quite primitive, I imagine your code will look different, but hopefully it makes some sense.