How to remove duplicates

Question

Hi
i am removing duplicate records while importing bulk data into the table...I am checking for some columns...when they are same, i am removing the old records...i have used the following code to remove duplicates...
execute immediate 'DELETE FROM test1 WHERE ROWID IN (SELECT ROWID FROM (SELECT ROWID,ROW_NUMBER() OVER (PARTITION BY c1,c2 ORDER BY 1) row_no FROM test1)WHERE row_no > 1)';
here i check c1 and c2 columns...if they are same the old records are to be deleted...but in this code, the new records are deleted..can anyone say how to remove old duplicate records?
Vally

Answer 1

Hi
i am removing duplicate records while importing
bulk data into the tableWhat you mean by using "while"?
During the process of importing(read inserting) - you want to delete duplicate records?
As you say in the following you have C1 and C2 - using both of them - you find duplicates.
I deem you have other columns besides C1 and C2. And these columns have different fileds in NEW record and OLD record - then why don't you use UPDATE statement?
...I am checking for some
columns...when they are same, i am removing the old
records...i have used the following code to remove
duplicates...you should clarify on what criteria you separate old records from new records and place this condition in your query.
E.g. you have a field DATE_OF_ENTRY
and the latest one is the new record which shouldn't be deleted
then you would be able to put it into your delete statement:
DELETE FROM test1
WHERE ROWID IN (SELECT ROWID
                   FROM (SELECT ROWID,
                                ROW_NUMBER() OVER(PARTITION BY c1, c2 ORDER BY DATE_OF_ENTRY desc) row_no
                           FROM test1)
                  WHERE row_no > 1)