Hi Davyjones,
You mentioned joining in SQL, so if you really need to do things in SQL, ask a Microsoft Partner to create a RecordID field type in the item table and update it with the associated value of the Item record with a processing only report.
Let me know if you need help with that.
Also on insert event of the item table this field needs to be populated. you can use these functions, just that I update a variable there instead of a new field.

That will give you the relation you need for SQL joins.
Cheers,
Robert
Please verify my answer, if you find it useful, that way others can find this solution easier!