How to exclude rows that don't join with another table?

Question

I have two tables, one has primary key other has it as a foreign key.

I want to pull data from the primary table, only if the secondary table does not

Answer 1

SELECT
   *
FROM
   primarytable P
WHERE
   NOT EXISTS (SELECT * FROM secondarytable S
     WHERE
         P.PKCol = S.FKCol)

Generally, (NOT) EXISTS is a better choice then (NOT) IN or (LEFT) JOIN