Null values get matched in Full Outer Join query. Can we stop this?

Null values would get matched in a full outer join in normal SQL, it's the same as a left join and a right join. You'd want Inner join for only matching rows.

As to why PQ matches on null (which it seems to do), I've no idea - you could put a dummy emp id in to fix it so -1 for example in one table

Hi Kyle,

Thank you very much for your answer. You know I am embarrassed to say it but actually it never occurred to me to assign a dummy empty ID. Very good tip and I am sure it will do the trick.
In the past I have successfully used Full Outer Joins without repeating empty cells but the caveat is that they had multiple matching columns. The multiple column criteria produced zero probability (in my case) of multiple null rows matching and therefore I never faced this issue before.

Going forward I think your tip is great and from now on I will assign different "Empty" IDs to each table just to be on the safe side.

Thank you very much.