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jmiller on 02/25/10

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Last Edited at 02/25/10 04:29pm

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Finding duplicates with SQL

/ Published in: SQL

Here's a handy query for finding duplicates in a table.

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# Suppose you want TO find ALL email addresses IN a TABLE that exist more than once:
 
SELECT email, 
 COUNT(email) AS COUNT
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 )