How to reference a list that matches the specific row

[Krismar]

I have table "Database" with columns "Item code", "item name", "quantity" etc.
The second table is "Shop" with columns "item code", "quantity" etc.
I need to reference the list of quantities while item codes match each other.

Appsheet does not let to use list expression in app formula if column type is "ref", so I 
tried the formula in "Valid if" field. 

select(
Database[quantity], [Item code]=[_thisrow].[Item code]
)

Unfortunately nothing happens. "quantity" column in "shop" table is still empty, nothing gets referenced.

[Aurelien · Accepted solution]

Hi @Krismar 

I think there is a confusion: you have "quantity" both in Database and Shop.

Can you try this:

[Related SHOPs][quantity]

Please note this expression should be used in the table Database.

This assumes the column "Item Code" in the SHOP table is set with type Ref and data source Database.