Compare and return difference between two tables in Windows Application

Hello.

I have developed one windows application in that application i have to show cutsomer data which do not paid for current month

I have two sql tables one is cutomer_data table and another is paid_reciept table.

Now I have to compare all cutomer_data table records with paid_reciept table records to get customer data who have not paid bill for current month.

How to get this data using c# and sql