I need to Group my Table into 15 minutes Intervals. I can do that with:

```
select dateadd(minute, datediff(minute, 0, ts) / 15 * 15, 0), sum (goodpieces) 
from StationCount 
Group by dateadd(minute, datediff(minute, 0, ts) / 15 * 15, 0)

```

But to display the returned data in a chart i need to insert also the intervals which don't have any data and aren't currently appearing in my select statement. How do i insert these?