Delete the data based on last updated date

Question

Hi ,
I have sample data like below.I want to delete the duplicate record but want to keep the latest record in the table.
Assumptions:-- There are milion of records so I do not know the last_updated_date for the duplicate record
EMP_NUMBER     LAST_UPDATE_DATE
555954116     12/2/2008 9:28:54 PM
555954116     9/7/2008 5:16:27 AM
555954116     9/7/2008 5:16:27 AM
555954116     9/7/2008 5:16:27 AM
555954116     9/7/2008 5:16:27 AM
555954116     9/7/2008 5:16:27 AM
555954116     9/7/2008 5:16:27 AM
Please suggest some idea.
Regards
Das

Answer 1

Delete can be performed in two ways:
1. Standard method to delete duplicates: Is good when number of duplicates are very small otherwise generates lot of UNDO/REDO logs.
DELETE FROM emp a
WHERE EXISTS ( SELECT NULL
                         FROM emp b
                         WHERE a.emp_number = b.emp_number
                         AND      a.last_update_date < b.last_update_date
{code}
2.  Copy-Paste : Is good when table is huge and a lot of duplicates as generate relatively less UNDO/REDO.
{code:sql}
-- Create table emp_temp having same structure/constraint/privilleges as original emp table
CREATE TABLE emp_temp....DDL
-- Copy latest employee record to temporary table
INSERT INTO emp_temp(emp_number, last_update_date)
SELECT emp_number, max(last_update_date) last_update_date
FROM emp
GROUP by emp_number;
-- Drop original employee table.
DROP TABLE emp CASCADE CONSTRAINT PURGE;
-- Rename emp_temp to emp
RENAME emp_temp to emp;
{code}