I want to know if there is any easy way to retrieve the difference of $$$ for two records that share the same ID, just that makes reference to different months.
ex
id-code-amount-date
1--a--$30 ---01/07
2--a--$40---02/07
3--b--$10---01/07
4--b--$25---02/07

I want the report to give me the difference by dates applied by the user


ex for the code a would be 40-30=10
b would be25-10=15

is there any easy way to do it????

I'm new on this, and is very easy to add the sum[field] to show everything, but not to show difference