Find duplicate records in MySQL

Question

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 >         


        

Answer 1

select `cityname` from `codcities` group by `cityname` having count(*)>=2

This is the similar query you have asked for and its 200% working and easy too. Enjoy!!!

Answer 2

Another solution would be to use table aliases, like so:

SELECT p1.id, p2.id, p1.address
FROM list AS p1, list AS p2
WHERE p1.address = p2.address
AND p1.id != p2.id

All you're really doing in this case is taking the original list table, creating two pretend tables -- p1 and p2 -- out of that, and then performing a join on the address column (line 3). The 4th line makes sure that the same record doesn't show up multiple times in your set of results ("duplicate duplicates").

Answer 3

This will select duplicates in one table pass, no subqueries.

SELECT  *
FROM    (
        SELECT  ao.*, (@r := @r + 1) AS rn
        FROM    (
                SELECT  @_address := 'N'
                ) vars,
                (
                SELECT  *
                FROM
                        list a
                ORDER BY
                        address, id
                ) ao
        WHERE   CASE WHEN @_address <> address THEN @r := 0 ELSE 0 END IS NOT NULL
                AND (@_address := address ) IS NOT NULL
        ) aoo
WHERE   rn > 1

This query actially emulates ROW_NUMBER() present in Oracle and SQL Server

See the article in my blog for details:

• Analytic functions: SUM, AVG, ROW_NUMBER - emulating in MySQL.

Answer 4

I tried the best answer chosen for this question, but it confused me somewhat. I actually needed that just on a single field from my table. The following example from this link worked out very well for me:

SELECT COUNT(*) c,title FROM `data` GROUP BY title HAVING c > 1;

Answer 5

SELECT t.*,(select count(*) from city as tt where tt.name=t.name) as count FROM `city` as t where (select count(*) from city as tt where tt.name=t.name) > 1 order by count desc

Replace city with your Table. Replace name with your field name