Relationships and ID Columns

Hi,

Ive seen this question asked before and it went in one ear and out the other,

If i had two or more queries (Sharepoint databases) that all use the one id (in my case its an Asset which is a unique code for ever piece of machinery), how come i cannot use this if one of my column contains several instants of the this unique Asset name

For example i have a database that stores everything about the Asset (Asset Register) and several others that use that to create work orders related to that asset, i.e Open work orders (a list of all tasks being completed on that machine at the moment) and closed work orders (completed work orders).

How come i cannot use a slicer for Assets to have two tables using asset register as the slicer and open and closed work orders (i get errors when there is many open work orders with the same Asset name)