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 Table_A A
LEFT JOIN Table_B B
ON A.Key = B.Key
WHERE B.Key IS NULL

Full image of join

From aticle : http://www.codeproject.com/KB/database/Visual_SQL_Joins.aspx