How to get Leave Category and total leave day by EmployeeId

I have Employee Table, LeaveCatagory Table, EmpLeave Table, Payroll Table. LeaveCatagory have Id,Category attribute. EmplLeave have Id, EmployeeId, LeaveCatagory Id. Payroll have Id,EmployeeId,LeaveCatagoryId. Now please give me solution how can I implement this program. In my interface I used combobox for every field. LeaveCatagory have to field, Formal Leave, Casual Leave. When User select employee Id, the system automatically generate Casual Leave from LeaveCategory combo box,and calculate all leave days of this employe in this month.