trying to exclude something from table

[jeff5656]

I want to run a query on table 1 but exclude records if the field v3 matches the field "mrn" in table 2:

 

I was told to use LEFT OUTER JOIN but this doens't work:

 

Code: 
SELECT * FROM pts LEFT OUTER JOIN p_list ON pts.v3 = p_list.mrn WHERE pts.v3 IS NULL

 

When I do that nothing is displayed.  I don't know if the "IS NULL" term is the problem.  Can someone help me with what the php code is to make that query work?

 

[OOP]

What are the keys in both tables? it would be good if you can post the tables structures