Finding Duplicates in a Table

Tags

duplicate rows, duplicate values, find duplicates, occurences, SQL Server, sql table

Here’s a handy query for finding duplicates in a table. Suppose you want to find all email addresses in a table 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 )

For further reading:
http://support.microsoft.com/default.aspx?scid=kb;en-us;139444
http://code.msdn.microsoft.com/SQLExamples/Wiki/View.aspx?title=DuplicateRows&referringTitle=Home