PHP: Selecting, grouping, and showing only arrays with the same key value?

Question

I have a MySQL database that holds log data from a vehicle's OBD-II reader. The application that interfaces with the reader collects a large amount (usually well over 2,000) of data point sets. Each of these data point sets gets its own row in the table, resulting in something like this:

+---------------+----------------------------------+---------------+----+----+-----+
| session       | id                               | time          | kd | kf | ... |
+---------------+----------------------------------+---------------+----+----+-----+
| 1420236074526 | 5cff4a3cc80b22cecb7de85266b25355 | 1420236074534 | 14 | 8  | ... |
| 1420236074526 | 5cff4a3cc80b22cecb7de85266b25355 | 1420236075476 | 17 | 8  | ... |
| 1420236074526 | 5cff4a3cc80b22cecb7de85266b25355 | 1420236075476 | 19 | 8  | ... |
| 1420236074526 | 5cff4a3cc80b22cecb7de85266b25355 | 1420236075476 | 23 | 8  | ... |
| 1420236074526 | 5cff4a3cc80b22cecb7de85266b25355 | 1420236077477 | 25 | 8  | ... |
+---------------+----------------------------------+---------------+---------+-----+

k5 and kf are the vehicle data types (vehicle speed and ambient air temperature, respectively).

There are two indexes in this table (which is called raw_logs ):

• session maps to columns session and id
• id maps to column id

What I'd like to do is grab all of the rows that have the same timestamp ( 1420236074526 , for example), and lump them together into a "session". The goal here is to create a select list where I can view data by session. Ideally, I'd have something like this as the output:

<select>
  <option>January 1, 2015 - 7:43AM</option>
  <option>January 1, 2015 - 5:15PM</option>
  <option>January 2, 2015, - 7:38AM</option>
  ...
</select>

---

This is what I have so far (I'm using Medoo to try and simplify the queries):

$session = $database->query("SELECT * FROM raw_logs USE INDEX (session)");

$sessionArray = array();
foreach($session as $session){
  $s_time = $session["session"];
  $sessionArray[$s_time] = array(
    "vehicle_speed" => $session["kd"],
    "ambient_air_temp" => $session["kf"]
  );
} print_r($sessionArray);

This works... sort of. I get the session time as the array and kd and kf under that with the correct key/value pairs, but it doesn't seem to want to iterate through the whole thing. There are around 25,000 rows in the table at the moment, but it's only returning a few, and there doesn't seem to be any logical order to the listing... it'll return two results from January 8th, one from the 9th, 4 from the 10th, etc.

---

What would be the best way to select all sessions with the same time stamp, group them, and create a selectable object that will only display the data for the given session?

Answer 1

If you are not ordering the query, there likely won't be any logical order to the listing. Also, you are overwriting the session data where duplicate values exist in the session column. You likely want to do something like $sessionArray[$s_time][] = array(... to append each row under the session id. Also, if you are having trouble, it is best to limit the results from your query down to like 20-100 and keep massaging until you get the result you want.