Question

My table consist of columns StartTime and EndTime with datetime datatype. I have calculated the duration from this two columns using this query:

SELECT   
   StartTime, EndTime, 
   DATEDIFF(s, StartTime, EndTime) AS duration 
FROM tbl_record 
WHERE StartTime >= @starttime AND StartTime < @endtime 
ORDER BY StartTime DESC 

How can I calculate the total sum of duration in sql query. This can be done using script but how to do in the database query? I have added something like

  SELECT SUM(duration) as total

Shows error:

duration invalid column

Answer 1

You can’t use an alias like that. You either have to use your original calculation in the sum and alias that as duration

SELECT   SUM(datediff(s,StartTime,EndTime)) as duration 
FROM     tbl_record 
where    StartTime >= @starttime 
         and StartTime < @endtime 

or use your original statement as a subselect to be able to use the duration alias in the outer select.

SELECT   SUM(duration)
FROM     (
          SELECT   datediff(s,StartTime,EndTime) as duration
          FROM     tbl_record 
          where    StartTime >= @starttime 
                   and StartTime < @endtime 
         ) d