SQL Server: Finding duplicate records in database table

Here's a handy query for finding duplicates in a table. Suppose you want to find all email addresses in a table name users that exist more than once:

SELECT email, 
COUNT(email) AS NumOccurrences
FROM users
GROUP BY email
HAVING ( 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 )

/Adnan


This post is from my old blog posted  on February 2011, that unfortunately no longer exist.