Delete duplicate rows from Oracle

shabbir's Avatar author of Delete duplicate rows from Oracle
This is an article on Delete duplicate rows from Oracle in Oracle.
There are times when duplicate rows somehow creep into the table. The best scenario to happen this is when the data is to be imported from some other table or data and the Constraints are removed so that data import successfully.

Now in Oracle you can delete the duplicate entries by just executing a simple SQL because Oracle stores an index to each row in a table known as ROWID

Code: SQL
CREATE TABLE duptest
  ( Id varchar(5),
  nonid varchar(5));
I create a table with just 2 fields. I dont have any constraint on ID because I would import some data which may be duplicated but after importing I would like to make the ID as PRIMARY KEY

Insert some date to simulate duplicates
Code: SQL
INSERT INTO duptest VALUES('1','a');
Insert them more than once.
Code: SQL
INSERT INTO duptest VALUES('2','b');
SQL to delete the duplicate rows
Code: SQL
DELETE FROM duptest WHERE rowid NOT IN (SELECT max(rowid) FROM duptest GROUP BY id);
Explanation :- In the subquery I Select a unique rowid from all the rowid's It can be MAX, MIN any one and the group by clause should include all the UNIQUE columns I desire. Say I want a composite primary key then the group by should be group by id1,id2 ...

The the subquery returns one record for the dupliacte ID's and I delete all of them that are not in the subquery and that deletes all the dupliacte rows from the database.
0
coderzone's Avatar, Join Date: Jul 2004
Team Leader
Thats good way to delete the rows.
0
lead.smart34's Avatar, Join Date: Feb 2008
Contributor
nice way
0
harminder's Avatar
Light Poster
a way to delete duplicate rows in oracle table You can also detect and delete duplicate rows using Oracle analytic functions:

delete from
customer
where rowid in
(select rowid from
(select
rowid,
row_number()
over
(partition by custnbr order by custnbr) dup
from customer)
where dup > 1);
0
kidas's Avatar, Join Date: Nov 2008
Go4Expert Member
Delete Duplicate Rows using Analytic functions
Code:
DELETE FROM TABLENAME
WHERE ROWID IN (SELECT ROWID FROM (SELECT ROW_NUMBER() OVER (PARTITION BY dup_col ORDER BY dup_col_1) rnk
                              	   FROM   TABLENAME)
                WHERE rnk>1);
0
Alok_1978's Avatar
Newbie Member
Incase if you want to check for all the columns then try this query:

delete from emp where rowid not in (select max(rowid) from emp group by id,name,no)

My emp table had 3 columns id,name,no and you need to group by all the columns in order to check if any column contains different value or not.if yes then that record will not be considered as duplicate and will not be deleted. The above query will delete the record only when all the columns have same value
0
rameshb's Avatar, Join Date: Dec 2010
Go4Expert Member
this is way to different from the way i have studies this is cool
0
TPrice's Avatar, Join Date: Aug 2010
Light Poster
Thank you for sharing this information. This is certainly a much easier way to go about it than the way I have been doing things. I wish I had known about this function a long time ago, it would have saved me a lot of extra work.
0
Tobiasgar's Avatar
Go4Expert Member
Usefull invention)) i think it's possible to delete much quicklier