Deleting Duplicate Rows
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Hello,
I have duplicate rows in a table such as this:
id donor_id
----------- -----------
933579 100009282
933580 100009282
933550 100020374
933549 100020374
933551 100029723
933552 100029723
Without anything unique to use in a DELETE statement, I cannot figure out how to delete these duplicate rows.
Can anyone offer a solution? I was thinking about using a CURSOR and checking the prev row to the curr row, but I ran into trouble accessing the field names.
Thanks in advance for your time,
Steve DiDomenico, Nashua, NH
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Create table #Tmp(Id int,Donor_ID int)
GO
Insert #Tmp
Select 933579, 100009282 union all
Select 933580, 100009282 union all
Select 933550, 100020374 union all
Select 933549, 100020374 union all
Select 933551, 100029723 union all
Select 933552, 100029723
GO
Select Min(tt.Id) as 'Min_ID',r.Donor_ID
from (Select Distinct t.Donor_ID from #Tmp as t) as r(Donor_ID)
Inner Join #Tmp as tt
On r.Donor_ID=tt.DOnor_ID
Group by r.Donor_ID
Order by r.Donor_ID
GO
Drop Table #Tmp
GO
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More Complete Solution!
Create table #Tmp(Id int,Donor_ID int)
GO
Insert #Tmp
Select 933579, 100009282 union all -- Multi duplicates
Select 933581, 100009282 union all
Select 933582, 100009282 union all
Select 933583, 100009282 union all
Select 933584, 100000000 union all -- Single
Select 933580, 100009282 union all
Select 933550, 100020374 union all
Select 933549, 100020374 union all
Select 933551, 100029723 union all
Select 933552, 100029723
GO
Delete from #Tmp
From (Select tt.Donor_ID,
Min(tt.Id) as 'Min_ID'
From #Tmp as tt
Group by tt.Donor_ID) as f(Donor_ID,Min_ID)
Where #Tmp.Donor_ID=f.Donor_ID
And #Tmp.ID<>f.Min_ID
GO
Select * from #Tmp Order by Donor_ID
GO
Drop Table #Tmp
GO
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One more way
DELETE
FROM #Tmp
WHERE Id IN
(
SELECT Id
FROM #Tmp
WHERE Id NOT IN
(
SELECT MAX(Cast(Id AS varchar(15)))
FROM #Tmp
GROUP BY Donor_ID
)
)
Thanks,
Ganesh
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I keep this terrific article Chris wrote in my virtual briefcase:
http://www.sqlservercentral.com/columnists/ccubley/findinganddeletingduplicatedata.asp
[font="Courier New"]ZenDada[/font]
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Thank you all for the posts.
I have a solution using the following sub select as a base and then additions to the WHERE clause:
(
SELECT MAX(Cast(Id AS varchar(15)))
FROM actual_table_name
GROUP BY donor_id
 
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Simple solution -- I do this all the time.
DELETE a
FROM t_table a
INNER JOIN t_table b
ON (
a.donor_id = b.donor_id AND
a.id > b.id)
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Simple and elegant.
I am at a loss to understand why we inherit such tables in the first place?! Primary Keys, Unique Constraints... these seem to be foreign concepts to some.
[font="Courier New"]ZenDada[/font]
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I've been using this one for quite some time. I like it because you can use it for combination keys (i.e. where the primary key is more than one column). Just substitute the key columns with fld1, fld1. (Also be sure to change the datatype for @fld1 and @fld2 as needed.)
/* You can delete your duplicates using a batch like:
(where fld1, fld2 are the fields that are the keys)
*/
DECLARE @Dups int, @fld1 int, @fld2 int
DECLARE Dups CURSOR FOR
SELECT fld1, fld2, COUNT(*) - 1 AS Duplicates
FROM Table1
GROUP BY fld1, fld2
HAVING COUNT(*) > 1
OPEN Dups
WHILE(1=1)
BEGIN
FETCH NEXT FROM Dups INTO @fld1, @fld2, @Dups
IF @@FETCH_STATUS < 0 BREAK
SET ROWCOUNT @Dups
DELETE Table1 WHERE fld1 = @fld1 And fld2 = @fld2
SET ROWCOUNT 0
END
DEALLOCATE Dups
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