abot

Hi. thanks for your help but i'm afraid i still don't understand how to set this up. I've read through several topics on global fields but i am not sure where to place certain items. i want to select the category within the service table so it can be repeatedly used without having to select the category time and again. I want the service to be selected in the line item which also selects the customer id to create the relationship. I dont understand what the global field should be and which fields it should be related to. and finally, how can i create an equation to calculate the sum of the line items of each category for an individual patient between a start date and end date. this is what my er diagram is so far thanks again

I'm very new to databse design and I need some help with a calculation that i'm working on i have 4 tables. customer, product, line item, and category The line item table is connected to the product, customer tables and the product table is connected to the category table and contains the pricing information i can get the sum of all the purchases made by a single customer but i am not sure how to get the sum of the purchases in a single category for each customer. any help on this is greatly appreciated thanks