This also can happen if at least on one of the tables your check constraint was created WITH NOCHECK.

You could insert your top 20 ActiveDirectory records into a temp table

and UNION separate selects...

Dave's query also can give you incorrect results because of the LEFT joins: you can get records where w.workphonenumber AS phone, w.emailaddress AS email,w2.workphonenumber AS phone, w2.emailaddress AS email ARE...

1) the killing you SCAN on WhitePaper is performed too many times because of the Nested Loop join used, so try adding :

OPTION(HASH JOIN, MERGE JOIN)

that will result in...

it could be a descent article had it been written 2 years ago.