If statement not working as expected with PHP sessions and SQL

So in my session is a table with various serial numbers that the user adds in. There is also a db with the information for that corresponding serial number.

What I want my code to do is, for each serial in the session, pull the corresponding data from the database. For now, I'll just echo a string.

So I figure to do that, you must loop through each serial in the session, and for each you must check if the same one exists in the db and if it does, then echo something.

The problem is that it works, but it only runs that last if loop once when I have more than one serial in the session.

Here's what gets echo'd out when you have 1,2,3 and 4 serials in the session. http://ift.tt/2eojolu

Any help would be greatly appreciated.

Code: http://ift.tt/2fNB530