Another "delete duplicate records" question

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Another "delete duplicate records" question

Author

Topic

Rasta Pickles
Posting Yak Master

174 Posts

Posted - 2012-09-01 : 11:20:26

I've just about got my head around using a CTE to delete duplicate records but can the syntax be extended to do a bit more?

I will explain

Assume I have a table called worklogs and one of the fields is named worklogid. I know there are going to be duplicate entries in this field but I have to be a bit clever in making sure I delete the right ones.

One of the other fields in this table is called CRNumber.

Now, here's the messy bit (to my novice brain anyway).....I have another table called orders and one of the fields is named CRNumber.

Is it possible to delete duplicate records from the worklogs table where the CRNumber field does NOT appear in the orders table (i.e I want to keep only records where there is an entry in the orders table)?

I started going down the route of


WHERE CRNumber NOT IN (SELECT CRNumber FROM orders)

but ended up confusing myself

Thanks in advance as always.

visakh16
Very Important crosS Applying yaK Herder

52326 Posts

Posted - 2012-09-01 : 12:37:20

[code]
FROM worklogs w
WHERE NOT EXISTS (SELECT 1 FROM orders WHERE CRNumber = w.CRNumber)
[/code]

------------------------------------------------------------------------------------------------------
SQL Server MVP
http://visakhm.blogspot.com/

Rasta Pickles
Posting Yak Master

174 Posts

Posted - 2012-09-01 : 12:52:13

Thank you, am I anywhere close with this?


;WITH cte AS
(SELECT ROW_NUMBER() OVER (PARTITION BY worklogid ORDER BY CRNumber) AS RN
FROM worklogs w
WHERE NOT EXISTS (SELECT 1 FROM orders WHERE CRNumber = w.CRNumber)

I'm not "feeling it" as the youth of Britain say......

visakh16
Very Important crosS Applying yaK Herder

52326 Posts

Posted - 2012-09-01 : 12:54:11

sorry why do you need a CTE here? you can have this in select itself

------------------------------------------------------------------------------------------------------
SQL Server MVP
http://visakhm.blogspot.com/

Rasta Pickles
Posting Yak Master

174 Posts

Posted - 2012-09-01 : 13:03:16

I'm still learning

My "safe" knowledge is that to delete duplicate rows you use a CTE?

Are you saying it's as simple as


DELETE FROM worklogs w
WHERE NOT EXISTS (SELECT 1 FROM orders WHERE CRNumber = w.CRNumber)

visakh16
Very Important crosS Applying yaK Herder

52326 Posts

Posted - 2012-09-01 : 13:04:18

yep...as per your requirement

------------------------------------------------------------------------------------------------------
SQL Server MVP
http://visakhm.blogspot.com/

Rasta Pickles
Posting Yak Master

174 Posts

Posted - 2012-09-01 : 14:54:36

Outrageously simple.

I will try it on Monday

visakh16
Very Important crosS Applying yaK Herder

52326 Posts

Posted - 2012-09-01 : 15:03:27

ok...np

let me know how you got on!

------------------------------------------------------------------------------------------------------
SQL Server MVP
http://visakhm.blogspot.com/

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