How to keep only one row of a table, removing duplicate rows?

Question

I have a table that has a lot of duplicates in the Name column. I\'d like to only keep one row for each.

The following lists the duplicates, but I don\'t know how to

Answer 1

if you want to remove duplicate record from table.

CREATE TABLE tmp SELECT lastname, firstname, sex
FROM user_tbl;
GROUP BY (lastname, firstname);

DROP TABLE user_tbl;

ALTER TABLE tmp RENAME TO user_tbl;

Answer 2

It would probably be easier to select the unique ones into a new table, drop the old table, then rename the temp table to replace it.

#create a table with same schema as members
CREATE TABLE tmp (...);

#insert the unique records
INSERT INTO tmp SELECT * FROM members GROUP BY name;

#swap it in
RENAME TABLE members TO members_old, tmp TO members;

#drop the old one
DROP TABLE members_old;

Answer 3

delete dup row keep one table has duplicate rows and may be some rows have no duplicate rows then it keep one rows if have duplicate or single in a table. table has two column id and name if we have to remove duplicate name from table and keep one. Its Work Fine at My end You have to Use this query.

DELETE FROM tablename
WHERE id NOT IN(

 SELECT id FROM
(
    SELECT MIN(id)AS id
    FROM tablename
    GROUP BY name HAVING 
    COUNT(*) > 1
)AS a )
AND id NOT IN(
(SELECT ids FROM
(
SELECT MIN(id)AS ids
    FROM tablename
    GROUP BY name HAVING 
    COUNT(*) =1
)AS a1
)
)

before delete table is below see the screenshot: enter image description here after delete table is below see the screenshot this query delete amit and akhil duplicate rows and keep one record (amit and akhil):

enter image description here

Answer 4

If we want to see first which rows you are about to delete. Then delete them.

with MYCTE as (
    SELECT DuplicateKey1
        ,DuplicateKey2 --optional
        ,count(*) X
    FROM MyTable
    group by DuplicateKey1, DuplicateKey2
    having count(*) > 1
) 
SELECT E.*
FROM MyTable E
JOIN MYCTE cte
ON E.DuplicateKey1=cte.DuplicateKey1
    AND E.DuplicateKey2=cte.DuplicateKey2
ORDER BY E.DuplicateKey1, E.DuplicateKey2, CreatedAt

Full example at http://developer.azurewebsites.net/2014/09/better-sql-group-by-find-duplicate-data/

Answer 5

You can join table with yourself by matched field and delete unmatching rows

DELETE t1 FROM table_name t1 
LEFT JOIN tablename t2 ON t1.match_field = t2.match_field
WHERE t1.id <> t2.id;

Answer 6

We have a huge database where deleting duplicates is part of the regular maintenance process. We use DISTINCT to select the unique records then write them into a TEMPORARY TABLE. After TRUNCATE we write back the TEMPORARY data into the TABLE.

That is one way of doing it and works as a STORED PROCEDURE.