Comments on: Mysql Remove Duplicate Data or Rows With DISTINCT

By: Chicago Web

Chicago Web — Tue, 17 Jan 2012 03:26:56 +0000

Here is a much faster solution for large tables…. The other methods will take hours on a very large table.

First we make a new table with distinct values for the field we are trying to remove duplicates for.

CREATE TABLE new_table as
SELECT * FROM old_table WHERE 1 GROUP BY column_to_remove_duplicates;

Step 2: remove old table

DROP TABLE old_table;

Step 3: mv the new table back to the old one

RENAME TABLE new_table TO old_table;

Done!

By: neeraj

neeraj — Mon, 16 Jan 2012 08:16:40 +0000

I like to below query if there is need to remove duplicate rows of table that does not contain primary key:

DELETE FROM items WHERE GREATEST(0,@num := IF(NAME = @NAME, @num + 1, 0),LEAST(0, LENGTH(@NAME := NAME)))>0

In my example items table just has one column “name” and above query removes the duplicate rows

By: Shairyar

Shairyar — Thu, 29 Dec 2011 09:07:16 +0000

great thanks, exactly what i was looking for.

By: John Ortiz

John Ortiz — Thu, 22 Dec 2011 14:56:59 +0000

Thanks a lot for this mini-guide. It was useful for me.

By: bob

bob — Tue, 13 Dec 2011 05:19:06 +0000

DELETE FROM table
 WHERE ID NOT IN (SELECT *
                    FROM (SELECT MIN(n.ID)
                            FROM table n
                        GROUP BY n.FIELDNAME) x)

By: John Komla

John Komla — Thu, 08 Dec 2011 12:17:10 +0000

This saved my day. I even customized this to fit my project, as different users insert into that same table, only records attached to a particular logging session are removed from the table.

This works great !

Thank you again !

By: ganesh

ganesh — Fri, 02 Dec 2011 05:54:03 +0000

hey guys this work thanks………..

By: kaushik

kaushik — Thu, 01 Dec 2011 09:24:46 +0000

thanx jafar..that is gr8 man..:)

By: Afshin

Afshin — Thu, 17 Nov 2011 21:07:51 +0000

All of you assume that there is a unique ID or we can create a new table!
Let’s say there is no ID and there is just one or two columns, and we don’t want to create a new table!

any idea?

By: sane

sane — Thu, 10 Nov 2011 11:31:26 +0000

!!!!! I need synatax in mysql !!!!!!

i create a table called studentaccount
if i create a row at the end one column called “status” should hav value boolean value as true

if i delete a row the status should be false

what is the syntax plzzzz help me

By: vikingu

vikingu — Thu, 13 Oct 2011 10:16:17 +0000

i’ll test at first, but looks like should workout!!

By: manish

manish — Sun, 04 Sep 2011 04:51:36 +0000

thank you jafar bhayi .

By: MANNULAL

MANNULAL — Fri, 26 Aug 2011 13:32:21 +0000

IT IS THE WAY OF HELPING EACH OTHER

By: kalaivani

kalaivani — Thu, 07 Jul 2011 09:38:38 +0000

Hi frnd,
your query is gud, but i have one doubt while i’m deleting…….
Suppose if i have two or more table and if that table contain more than 80000 records, and i find some duplicate records in my table & try to delete them means the other table will be suffer or not? because i kept all id’s as primary key & set to other table into foreign key, while i’m deleting a primary key, Will foreign key show error? or will other table be suffered?

By: Ricky

Ricky — Thu, 07 Jul 2011 04:05:15 +0000

WOW your the MAN!!

I used exactly what you said and then i checked with

SELECT field_name,
COUNT(field_name) AS NumOccurrences
FROM cron_jobs
GROUP BY field_name
HAVING ( COUNT(field_name) > 1 )

Worked like a charm!!

By: overseer

overseer — Mon, 16 May 2011 09:56:54 +0000

Totally awesome.

By: Jim

Jim — Fri, 06 May 2011 01:39:49 +0000

TRUNCATE TABLE bar WHERE duplicate IS true;

By: mkquake

mkquake — Mon, 02 May 2011 18:59:10 +0000

Sure, if you are working with 80286 !

By: choudhury

choudhury — Fri, 18 Mar 2011 03:00:42 +0000

wow! This really worked for me…Thanks a lot Gerald…
—
DELETE FROM `MyTable`
WHERE `DuplCol` IN (
SELECT `DuplCol`
FROM (

SELECT `DuplCol` , count( * ) AS c
FROM `MyTable`
GROUP BY `DuplCol`
HAVING c >1
) AS dctbl
)
AND `id` NOT IN (
SELECT `mi`
FROM (
SELECT `DuplCol` , min( `id` ) AS mi
FROM `MyTable`
GROUP BY `DuplCol`
) AS idtbl
);

By: brij

brij — Wed, 16 Mar 2011 13:12:43 +0000

DELETE FROM vehicle_makes USING vehicle_makes,
vehicle_makes AS vtable WHERE (
NOT vehicle_makes.id = vtable.id
) AND (
vehicle_makes.name = vtable.name
)

=====================
id name
=====================
2 Ottawa
3 AM General/Hummer
5 John Deere
4 WRV 6 WRV
17 Blue Bird
20 Chance
21 Crane Carrier
22 Crane Carrier
======================