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delete duplicate data

Posted on 2016-09-23
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Last Modified: 2016-09-26
I need to delete duplicate data
i.e. if i have 2 rows exactly the same, delete one of the rows

I have a table called Tbl_Data
It has these columns

ID
GPSDateTime (datetime)
ReportID (int)
DeviceID (int)

If all 3 columns match data (except ID) I want to delete one of the rows so i'm left with unique data rows instead duplicates

how might i Do this?
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Question by:websss
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4 Comments
 
LVL 70

Accepted Solution

by:
Scott Pletcher earned 2000 total points
ID: 41812808
For best performance, if the table has an index with all three of those columns in it, and is keyed by one or more of them, start with column first in the PARTITION BY.
For example, say there was an index on ( ReportID, GPSDateTime ) that included ( DeviceID ), then you would ORDER BY ReportID, GPSDateTime, DeviceID.  The idea is to use any existing "pre-sorting" as much as possible.


;WITH cte_dups AS (
    SELECT *, ROW_NUMBER() OVER(PARTITION BY GPSDateTime, ReportID, DeviceID) AS row_num
    FROM Tbl_Data
)
DELETE FROM cte_dups
WHERE row_num > 1
0
 

Author Comment

by:websss
ID: 41813395
Thanks Scott

I'm getting the errror:

Msg 4112, Level 15, State 1, Line 2
The function 'ROW_NUMBER' must have an OVER clause with ORDER BY.
0
 

Author Closing Comment

by:websss
ID: 41813418
Got it thanks
0
 
LVL 70

Expert Comment

by:Scott Pletcher
ID: 41816242
Yeah, sorry, I left out the ORDER BY, which must appear, even if it's meaningless:

;WITH cte_dups AS (
    SELECT *, ROW_NUMBER() OVER(PARTITION BY GPSDateTime, ReportID, DeviceID ORDER BY GPSDateTime) AS row_num
    FROM Tbl_Data
)
DELETE FROM cte_dups
WHERE row_num > 1
0

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