Subtotals and total keeping the details

Question

I have a table with invoices:

invoice_num, customer_ID, usd
1              A          15.2
2              B           3.6
3              A         105.1
4              C           6.0

I need a report showing all the records (invoices) and adding a subtotal per customer. I know how to do it if I just show the total per customer (with GROUP BY customer_ID and WITH ROLLUP) but I need to keep the details, so I can't group the lines. The desired output is:

invoice_num  customer_ID   usd
1              A          15.2
3              A         105.1
Total customer A         120.3
2              B           3.6
Total customer B           3.6
4              C           6.0
Total customer C           6.0
Total customers          129.9

Thanks,

Answer 1

Also group on invoice_num:

SELECT   invoice_num, customer_ID, SUM(usd)
FROM     my_table
GROUP BY customer_ID, invoice_num WITH ROLLUP

See it on sqlfiddle.