By saying requirements what do you mean?
It's a system for Car sales management....
Basically the relationship I'm mostly not sure of is the one between the SaleItem and TBLservices & TBLCars...I want the user to enter the id of the item sold, but i want it to be taken from 2 different tables....like when someone buys a car, he'll enter the CarID in the same field he'd enter the serviceid if he bought a service...
I hope I managed to explain it
Yea, services and Car ... what if a customer wants to purchase both - he buys a car and purchases some service plan for the same car. Or already has a car and wants just to purchase some service. (Is it allowed?)
I suggest it should have two entities - both carid and serviceid - preferably optional.
Both are independent of each other.
I assume the payment table is duplicated in the diagram.
But how do you distinguish carid from serviceid ?
ok, you have different sequence/series for both ids. But every time you get the id, you'll have to search two different places to determine whether it's a carid or a serviceid.
How will this be done in reports ?
You can have a flag indicating the type of id.
like .. if flag = 'C' then the id belongs to carid
if 'S' then it's a serviceid.