I have a table with a catalogue#, location and quantity. I want to combine all the similar catalogue#'s and have the new row's quantity be the sum of quantity of all the rows with that catalogue#.

For example if i have:

```
Catalouge#, Location, Quantity
1234, A, 5
1234, B, 10
1234, C, 10
4321, A, 2
4321, B, 3

```

I want to end up with:

```
Catalouge#, Location, Quantity
1234, null, 25
4321, null, 5

```

There are hundred of catalogue numbers so i cant do individual queries for each catalogue number. But that's the only way i can think to do it. Any body have a more generalized way to do it? I prefer to do it in sql but i could do it in c# if necessary.