Relationships between tables Purch_ Inv_ Line + Item Ledger Entry

mazheika

Hello!
I'm having trouble with two questions, please help:
1. How to find relationships between tables?
How to join them?
Purch_ Inv_ Header + Purch_ Inv_ Line + Item Ledger Entry
I am joining them on document_no
But for some reason, not all Purch_ Inv entries are appearing in the Item Ledger Entry
Documents in Purch_ Inv look like PPINV-00000076
In the Purch_ Inv_ Header table, I have 181 such documents, but only two have appeared in the Item Ledger Entry
What could be the reason for this? Please advise.

KTA8

Normally the entries are made by the receipt not by the invoice