Question

I have a SQLite Database with a table called “events”, it has the following structure:

rowid       ID                  startTimestamp   endTimestamp
1           00:50:c2:63:10:1a   1000             1010
2           00:50:c2:63:10:1a   1100             1030
3           00:50:c2:63:10:1a   1090             1110   
4           00:50:c2:63:10:1a   1210             1310
.
.
.

It’s no problem to calculate the average time between startTimestamp and endTimestamp:

SELECT ID, avg(endTimestamp - startTimestamp) AS duration FROM events WHERE senderID ="00:50:c2:63:10:1a"

But now i want to have the average differences between the endTime and the startTime between one row and the following row, that means for my example:

1100-1010 = 90

1090-1030 = 60

1210-1110 = 100

---

Sum of differences = 90 + 60 + 100 = 250

Average Difference = 250 / 3 = 83,33

Is there a way to do this with an SQL Query? Or should is it necessary to write a piece of code in PHP?

Answer 1

SELECT
    id,
    ( MAX(endtimestamp) - MIN(startTimestamp)
    - SUM(endtimestamp-startTimestamp)
    ) / (COUNT(*)-1) AS averageDifference
FROM
    events
GROUP BY
    id ;

Tested at SQL-Fiddle: test-1 (thanks to @bonCodigo for that)

---

Since the MIN(endtimestamp) may not be the one with lowest rowid, the above query needs a correction:

SELECT
    id,
    ( ( SELECT endtimestamp FROM events AS ee 
        WHERE ee.id = e.id ORDER BY rowid ASC LIMIT 1 )
    - ( SELECT startTimestamp FROM events AS ee
        WHERE ee.id = e.id ORDER BY rowid DESC LIMIT 1 )
    - SUM(endtimestamp-startTimestamp)
    ) / (COUNT(*)-1) AS averageDifference
FROM
    events AS e
GROUP BY
    id ;