Average time between sql edits in php - php

Question

I currently have a system to track inventory items.
The sql table is set up as follows:
Unique ID | Order number | Location | TimeStamp
Every time an order moves, a new entry is created with the same order number with the new location and timestamp.
Now I need to find the average time required for order to move from one location to another, say from Location Warehouse to Pickup Depot.
I am trying to work on the query and I have this so far.
SELECT
IFNULL(TIMESTAMPDIFF(SECOND,
MIN(TimeStamp),
MAX(TimeStamp)) / NULLIF(COUNT(*) - 1, 0), 0)
FROM TableName
WHERE Status = 'Delivered'
AND TimeStamp > DATE_SUB(NOW(), INTERVAL 6 HOUR)
The works really well if the table only had one order number, the moment we add more table numbers the average goes off.
I need it to only look at the timestamp difference for each order number, while currently I think its looking at the whole table.
Any help would be much appreciated.
Apologize for posting this question twice, the previous post did not contain enough information.
Thanks again.
SELECT
IFNULL(TIMESTAMPDIFF(SECOND,
MIN(TimeStamp),
MAX(TimeStamp)) / NULLIF(COUNT(*) - 1, 0), 0)
FROM TableName
WHERE Status = 'Delivered'
AND TimeStamp > DATE_SUB(NOW(), INTERVAL 6 HOUR)
GROUP BY OrderNumber
The above query returns the timedifference in different rows in sql (with the following error " Current selection does not contain a unique column. Grid edit, checkbox, Edit, Copy and Delete features are not available.". The table has one column named "IFNULL(TIMESTAMPDIFF(SECOND, MIN(TimeStamp), MAX(TimeStamp)) / NULLIF(COUNT(*) - 1, 0), 0)" with the time difference for various orders arrange in rows. Now I am trying to get their average with the output code.
Am outputting the results with the following code:
$row_cnt = $result2->num_rows;
while ($row2 = mysqli_fetch_assoc($result2)) {
$processingseconds = $row2['IFNULL(TIMESTAMPDIFF(SECOND, MIN(TimeStamp), MAX(TimeStamp)) / NULLIF(COUNT(*) - 1, 0), 0)'] + $processingseconds;
}
print "Current Processing Time: ";
$processingseconds = $processingseconds/$row_cnt;
$processingminutes = $processingseconds/60;
echo $processingminutes;

Answer 1

Try adding a Group by condition to your query.
GROUP BY Order_Number_column
Something like this:
SELECT
IFNULL(TIMESTAMPDIFF(SECOND,
MIN(TimeStamp),
MAX(TimeStamp)) / NULLIF(COUNT(*) - 1, 0), 0)
FROM TableName
WHERE Status = 'Delivered'
AND TimeStamp > DATE_SUB(NOW(), INTERVAL 6 HOUR)
GROUP BY Your_Order_Number_column