Inconsistent Data When Using Relationship on Index column between a Merged Table and a Source Table

Hi carrienorris my best practice when I merge columns in PQ: write number of rows before any "transformation" per table / columns. During merging if you notice PQ inform you how many rows are mathed from one table to another one. If counting rows before and after merging do not fit / make sense then depending on your need change type of join (left to rights etc) and for sure check are there in columns some blank rows or similar. 

Sometimes, it is expected to have "lower" number of matched rows between tables as it is possible that like some products are never /not sold but this product is in catalogue. I hope this help