Chris Bartow Chris Bartow - 7 months ago 25
SQL Question

Find duplicate records in MySQL

I want to pull out duplicate records in a MySQL Database. This can be done with:

SELECT address, count(id) as cnt FROM list
GROUP BY address HAVING cnt > 1


Which results in:

100 MAIN ST 2


I would like to pull it so that it shows each row that is a duplicate. Something like:

JIM JONES 100 MAIN ST
JOHN SMITH 100 MAIN ST


Any thoughts on how this can be done? I'm trying to avoid doing the first one then looking up the duplicates with a second query in the code.

Answer

The key is to rewrite this query so that it can be used as a subquery.

SELECT firstname, 
   lastname, 
   list.address 
FROM list
   INNER JOIN (SELECT address
               FROM   list
               GROUP  BY address
               HAVING COUNT(id) > 1) dup
           ON list.address = dup.address;