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Problem deleting duplicates using a CTE when there are table joins

Posted on 2010-11-10
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Last Modified: 2012-05-10
I've used CTEs to remove duplicates successfully before, but this time round I wanted to delete them from one table having joined to other tables and it comes back with the error:

View or function 'dupnotesCTE' is not updatable because the modification affects multiple base tables. See the attached code for my sql statement.

Not sure where I've gone wrong here...can someone help please?
;WITH dupnotesCTE([FileNo]
      ,[CommentDate]
      ,[CommentTime]
      ,[CommentUser]
      ,[Cat]
      ,[Pri]
      ,[Line]
      ,[Note], Ranking)
AS
(
SELECT	p.[FileNo]
      ,p.[CommentDate]
      ,p.[CommentTime]
      ,p.[CommentUser]
      ,p.[Cat]
      ,p.[Pri]
      ,p.[Line]
      ,p.[Note]
	,Ranking = row_number() OVER(PARTITION BY p.[FileNo]
      ,p.[CommentDate]
      ,p.[CommentTime]
      ,p.[CommentUser]
      ,p.[Cat]
      ,p.[Pri]
      ,p.[Line]
      ,p.[Note] ORDER BY p.[FileNo]
      ,p.[CommentDate]
      ,p.[CommentTime]
      ,p.[CommentUser]
      ,p.[Cat]
      ,p.[Pri]
      ,p.[Line]
      ,p.[Note])
FROM filenotes p
join detailtable d on ltrim(rtrim(p.FileNo)) = ltrim(rtrim(d.FileNo))
join country c on d.country_no = c.country_no
where c.continent in ('Asia','Europe')
)

delete from dupnotesCTE
where ranking > 1

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0
Comment
Question by:Grffster
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10 Comments
 
LVL 32

Expert Comment

by:Erick37
ID: 34101354


...

delete p
FROM filenotes p
JOIN dupnotesCTE c ON c.FileNo = p.fileNo --??
where c.ranking > 1
0
 

Author Comment

by:Grffster
ID: 34101830
This won't work though will it as, say you have a pair of duplicates A and B. You have A in dupnotesCTE with rank 1, and B in dupnotesCTE with rank 2. When you link from filenotes to dupnotes you'll have 4 records:

filenotes.A and dupnotes.A (rank 1)
filenotes.A and dupnotes.B (rank 2)
filenotes.B and dupnotes.A (rank 1)
filenotes.B and dupnotes.B (rank 2)

Your "where c.ranking > 1" will remove the 2nd and 4th combinations but you're left with two records i.e. combinations 1 and 3 above.

May be mistaken, but my query seems to reflect this.
0
 
LVL 32

Expert Comment

by:Erick37
ID: 34102171
Does filenotes table have an identity column or primary key that you could use to join the cte?

0
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Author Comment

by:Grffster
ID: 34102188
No it doesn't sorry.
0
 
LVL 32

Expert Comment

by:Erick37
ID: 34102227
So all of the columns with the duplicate FileNo are also duplicate?
0
 

Author Comment

by:Grffster
ID: 34102264
Yes, all the fields per fileno duplicate are identical i.e. a true duplicated record with the same data in each column:

[FileNo],[CommentDate],[CommentTime],[CommentUser],[Cat],[Pri],[Line],[Note]
0
 
LVL 32

Expert Comment

by:Erick37
ID: 34102504
Having an identity column would greatly simplify identifying the duplicates.

One possibility would be to copy the records over to a temp table with an identity column.
Remove the duplicates from the temp table.
Delete all the records from the user table that you originally copied to the temp table.
Insert the cleaned records back into filenotes table.

Here are some other alternatives:
"How to delete duplicate records or rows among identical rows in a table where no primary key exists"
http://www.kodyaz.com/articles/delete-duplicate-records-rows-in-a-table.aspx
0
 

Author Comment

by:Grffster
ID: 34102929
I've added an identity column to the filenotes table now. How should it look now? Do I do something like at the bottom of your last link in method 3?
0
 
LVL 32

Accepted Solution

by:
Erick37 earned 2000 total points
ID: 34103157
You will add the identity column to the CTE and use that to join the table to the cte.

;WITH dupnotesCTE AS
(
  SELECT
      IdentityColumn
      ,[FileNo]
      ...
      ,row_number() OVER(PARTITION BY p.[FileNo] order by IdentityColumn) AS Ranking
     ...

)
delete p
FROM filenotes p
JOIN dupnotesCTE c ON c.IdentityColumn = p.IdentityColumn AND c.ranking > 1
0
 

Author Closing Comment

by:Grffster
ID: 34103515
That's worked a dream thanks Eric.
0

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