In this post I am going to discuss how to determine the difference between two table/ entity sets. Here's an example: we want to get rows form table_A which do not exist in table_B. (When table_A primarykey is part of table_B foreignkey).

What follows is a way to get the row(s) to form table_A which are not part of table_B

SELECT <select_list>
FROM Table_A A
LEFT JOIN Table_B B
ON A.Key = B.Key
WHERE B.Key IS NULL
</select_list>

In Linq to Sql you can achieve same thing just by calling one function exception.

var infoQuery =
    (from tblA in db.Table_A
    select tblA.Key)
    .Except
        (from tblB in db.Table_B
        select tblB.Key);

So by using above query you can easily achieve task of creating a difference between two entity sets.