We have a table set up as follows:

|ID|EmployeeID|Date     |Category       |Hours|
|1 |1         |1/1/2010 |Vacation Earned|2.0  |
|2 |2         |2/12/2010|Vacation Earned|3.0  |
|3 |1         |2/4/2010 |Vacation Used  |1.0  |
|4 |2         |5/18/2010|Vacation Earned|2.0  |
|5 |2         |7/23/2010|Vacation Used  |4.0  |

The business rules are:

• Vacation balance is calculated by vacation earned minus vacation used.
• Vacation used is always applied against the oldest vacation earned amount first.

We need to return the rows for Vacation Earned that have not been offset by vacation used. If vacation used has only offset part of a vacation earned record, we need to return that record showing the difference. For example, using the above table, the result set would look like:

|ID|EmployeeID|Date     |Category       |Hours|
|1 |1         |1/1/2010 |Vacation Earned|1.0  |
|4 |2         |5/18/2010|Vacation Earned|1.0  |

Note that record 2 was eliminated because it was completely offset by used time, but records 1 and 4 were only partially used, so they were calculated and returned as such.

The only way we have thought of to do this is to get all of the vacation earned records in a temporary table. Then, get the total vacation used and loop through the temporary table, deleting the oldest record and subtracting that value from the total vacation used until the total vacation used is zero. We could clean it up for when the remaining vacation used is only part of the oldest vacation earned record. This would leave us with just the outstanding vacation earned records.

This works, but it is very inefficient and performs poorly. Also, the performance will just degrade over time as more and more records are added.

Are there any suggestions for a better solution, preferable set based? If not, we'll just have to go with this.