Sum of a Column from one table to another


So I have three tables, Sales, Purchases & Inventory. I have 3 items A, B, C. In each sale, a customer can buy all three, just two or one of the items in whatever quantity they wish. On each day I make purchases of varying quantities of A, B & C. I cannot figure out how to use rollup to give me a total of purchases, sales and purchases - sales in my inventory. Images of my three tables below.

Hi @Coco_Custo,

Welcome to Airtable Community !

You cannot use Rollup in your current setup. In order to use Rollup, you need to Link a field first.

So instead of have a field for item A, Field for B, field for C, and so on, you should have 1 field that is Linked to you Inventory Table where you enter the item and the qty, then you can Rollup in Inventory.


Thank you for your response. To clarify. I would create a field called product ordered and link it to inventory. And then have another column for quantity? Would this limit my customers order to a single item? So if a customer places an order that includes A & B how could I resolve that?