Issue with Self join statement php

Question

Here is the line

$sql0 = "SELECT * FROM PMOrder a, PMList b where AssetNum= b.'$AssetNum';";

I get

You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near ''PQ0000357'' at line 1

I'm assuming I can do a select a from both tables and echo the results as needed or do I need to pull all the columns from both? first time using the self join.
A explanation of what I'm doing wrong would be greatly appreciated. Thanks in advance Corrected code

$sql0 = "SELECT * FROM PMOrder a, PMList b where b.AssetNum= '$AssetNum';";