In this tips I have discussed about how to get the difference between two table/ entity sets. As for example we want to get rows form table_A which are not exists in table_B. (When table_A primarykey is part of table_B foreignkey).
Following is way to get the row(s) form table_A which are not part of table_B
SELECT FROM Table_A A LEFT JOIN Table_B B ON A.Key = B.Key WHERE B.Key IS NULL
In Linq to Sql you can achieve same thing just by calling one function Except.
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 getting difference between set of collection.