• Here is some T-SQL to find duplicate column values.  Here is the link where I found the code : http://www.petefreitag.com/item/169.cfm

SELECT email,

COUNT(email) AS NumOccurrences

FROM users

GROUP BY emailHAVING ( COUNT(email) > 1 )

You could also use this technique to find rows that occur exactly once:

SELECT email

FROM users

GROUP BY email

HAVING ( COUNT(email) = 1 )
 

• An excellent post from Scott Guthrie on the Search Optimization Toolkit