What is the sort order and PK?

>
>May I know how to use the sql to count a record by grouping.
>example:
>
>Table A
>======
>Receipt DiscountDesc DiscountAmt
>1000 10% discount 10
>1000 20% discount 20
>1001 10% discount 10
>1002 50% discount 50
>1002 10% dsicount 10
>
>
>How to include the running number /counter in record by receipt group such as the output is:
>
>Receipt DiscountDesc DiscountAmt Counter
>1000 10% discount 10 1
>1000 20% discount 20 2
>1001 10% discount 10 1
>1002 50% discount 50 1
>1002 10% dsicount 10 2
>
>Thanks for your help in advance.