Maybe my brain is not working, but if you can return a set of punch in/outs for an employee, shouldn't you be able to use ROWNUMBER() to get odd (clock in) and even (clock out) records? Then you join odds to evens ( ON rn=rn-1), and then just subtract? Or is there a possibility that someone may not have clocked in/out on a given day? If you did that, you may not even need RowNumber, but you could use LAG instead... (just LAG by one to get the previous record.)