I want to add a primary key to a table with some duplicates and I have to get rid of them first, keeping the first row from each duplication case.
Say I found a case of duplication where there are 5 rows with t1.id=3. Other columns may be identical or not (I cannot count on it).
I'm looking for something like
delete top (5) * from t1 where not exists (select top (1) * from t1 where t1.id=3)
I'm looking for a solution that will not involve using creating additional identity column or copying to a table with this primary key set because this table may have huge amount of rows, and these options are too time consuming.
3  2808  Delerna 1,134
Recognized Expert Top Contributor
As this is a one off cleanup operation I suggest you resort to a cursor.
One thing concerns me,
you say the rest of the fields might be identical or they might not be.
This suggests to me the possibility of there being 2 or more records for a particular ID and that all of those records are completely identical.
If this is true then you have no way of identifying 1 of them over the others.
Either you will have to delete all of them and then re-insert 1 back, or you will have to add an identity field.
Delerna 1,134
Recognized Expert Top Contributor
Oh, by the way, I hope your going to take the time to make a backup copy of the table before you do this?
Thanks for your reply
I was given a solution on another place
with c as
(
select *, row_number() over(partition by id order by (select 0)) as n
from t1
)
delete from c
where n > 1;
However, I also need a solution for MsSQL 2000. Any ideas?
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