Update Cursor Advice

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Update Cursor Advice

SQL_Kills

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Points: 3154
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December 10, 2013 at 4:14 pm

#283396

Hi,
I have two tables Main & OrderReturn
CREATE TABLE [dbo].[Main](
[orderID] [varchar](15) NULL,
[orderLine] [int] NULL,
[mpn] [varchar](25) NULL
) ON [PRIMARY]
GO
CREATE TABLE [dbo].[OrderReturn](
[orderID] [varchar](15) NULL,
[orderLine] [int] NULL,
[mpn] [varchar](25) NULL
) ON [PRIMARY]
GO
insert into Main values ('EE170828',1,'ABC654081-B21CBA')
insert into Main values ('EE170828',2,'ABC654081-B21#B19CBA')
insert into Main values ('EE170828',3,'ABC654764-L21CBA')
insert into Main values ('EE170828',4,'ABC654764-B21CBA')
insert into Main values ('EE170828',5,'ABC654764-B21#0D1CBA')
insert into Main values ('EE170828',6,'ABC647893-B21CBA')
insert into Main values ('EE170828',7,'ABC647893-B21#0D1CBA')
insert into Main values ('EE170828',8,'ABC652564-B21CBA')
insert into Main values ('EE170828',9,'ABC652564-B21#0D1CBA')
insert into Main values ('EE170828',10,'ABC684208-B21CBA')
insert into Main values ('EE170828',11,'ABC661069-B21CBA')
insert into Main values ('EE170828',12,'ABC661069-B21#0D1CBA')
insert into Main values ('EE170828',13,'ABC734807-B21CBA')
insert into Main values ('EE170828',14,'ABC734807-B21#0D1CBA')
insert into Main values ('EE170828',15,'ABCAP770BCBA')
insert into Main values ('EE170828',16,'ABCAP770B#0D1CBA')
insert into Main values ('EE170828',17,'ABC656362-B21CBA')
insert into Main values ('EE170828',18,'ABC656362-B21#0D1CBA')
insert into Main values ('EE170828',19,'ABCC6N36ABECBA')
insert into Main values ('EE170828',20,'ABC654081-B21CBA')
insert into Main values ('EE170828',21,'ABC654081-B21#B19CBA')
insert into Main values ('EE170828',22,'ABC654764-L21CBA')
insert into Main values ('EE170828',23,'ABC654764-B21CBA')
insert into Main values ('EE170828',24,'ABC654764-B21#0D1CBA')
insert into Main values ('EE170828',25,'ABC647893-B21CBA')
insert into Main values ('EE170828',26,'ABC647893-B21#0D1CBA')
insert into Main values ('EE170828',27,'ABC652564-B21CBA')
insert into Main values ('EE170828',28,'ABC652564-B21#0D1CBA')
insert into Main values ('EE170828',29,'ABC684208-B21CBA')
insert into Main values ('EE170828',30,'ABC661069-B21CBA')
insert into Main values ('EE170828',31,'ABC661069-B21#0D1CBA')
insert into Main values ('EE170828',32,'ABC734807-B21CBA')
insert into Main values ('EE170828',33,'ABC734807-B21#0D1CBA')
insert into Main values ('EE170828',34,'ABCAP770BCBA')
insert into Main values ('EE170828',35,'ABCAP770B#0D1CBA')
insert into Main values ('EE170828',36,'ABC656362-B21CBA')
insert into Main values ('EE170828',37,'ABC656362-B21#0D1CBA')
insert into Main values ('EE170828',38,'ABCC6N36ABECBA')
insert into Main values ('EE170828',39,'ABC654081-B21CBA')
insert into Main values ('EE170828',40,'ABC654081-B21#B19CBA')
insert into Main values ('EE170828',41,'ABC654780-L21CBA')
insert into Main values ('EE170828',42,'ABC647897-B21CBA')
insert into Main values ('EE170828',43,'ABC647897-B21#0D1CBA')
insert into Main values ('EE170828',44,'ABC652564-B21CBA')
insert into Main values ('EE170828',45,'ABC652564-B21#0D1CBA')
insert into Main values ('EE170828',46,'ABC684208-B21CBA')
insert into Main values ('EE170828',47,'ABC661069-B21CBA')
insert into Main values ('EE170828',48,'ABC661069-B21#0D1CBA')
insert into Main values ('EE170828',49,'ABC734807-B21CBA')
insert into Main values ('EE170828',50,'ABC734807-B21#0D1CBA')
insert into Main values ('EE170828',51,'ABC656362-B21CBA')
insert into Main values ('EE170828',52,'ABC656362-B21#0D1CBA')
insert into Main values ('EE170828',53,'ABCC6N36ABECBA')
insert into Main values ('EE170828',54,'ABCU4497ECBA')
insert into OrderReturn values ('EE170828',0,'ABC734807-B21CBA')
insert into OrderReturn values ('EE170828',0,'ABC647893-B21CBA')
insert into OrderReturn values ('EE170828',0,'ABC652564-B21CBA')
insert into OrderReturn values ('EE170828',0,'ABC656362-B21CBA')
insert into OrderReturn values ('EE170828',0,'ABC654081-B21#B19CBA')
insert into OrderReturn values ('EE170828',0,'ABCU4497ECBA')
insert into OrderReturn values ('EE170828',0,'ABC734807-B21CBA')
insert into OrderReturn values ('EE170828',0,'ABC661069-B21CBA')
insert into OrderReturn values ('EE170828',0,'ABC734807-B21CBA')
insert into OrderReturn values ('EE170828',0,'ABC654764-L21CBA')
insert into OrderReturn values ('EE170828',0,'ABC647893-B21CBA')
insert into OrderReturn values ('EE170828',0,'ABC652564-B21CBA')
insert into OrderReturn values ('EE170828',0,'ABCAP770B#0D1CBA')
insert into OrderReturn values ('EE170828',0,'ABC652564-B21CBA')
insert into OrderReturn values ('EE170828',0,'ABCC6N36ABECBA')
insert into OrderReturn values ('EE170828',0,'ABC654081-B21CBA')
insert into OrderReturn values ('EE170828',0,'ABC656362-B21#0D1CBA')
insert into OrderReturn values ('EE170828',0,'ABC647897-B21CBA')
insert into OrderReturn values ('EE170828',0,'ABC654081-B21#B19CBA')
insert into OrderReturn values ('EE170828',0,'ABC661069-B21CBA')
insert into OrderReturn values ('EE170828',0,'ABC661069-B21CBA')
insert into OrderReturn values ('EE170828',0,'ABCC6N36ABECBA')
insert into OrderReturn values ('EE170828',0,'ABC647897-B21#0D1CBA')
insert into OrderReturn values ('EE170828',0,'ABC654764-B21CBA')
insert into OrderReturn values ('EE170828',0,'ABC647893-B21#0D1CBA')
insert into OrderReturn values ('EE170828',0,'ABC661069-B21#0D1CBA')
insert into OrderReturn values ('EE170828',0,'ABCC6N36ABECBA')
insert into OrderReturn values ('EE170828',0,'ABC654764-B21#0D1CBA')
insert into OrderReturn values ('EE170828',0,'ABCAP770BCBA')
insert into OrderReturn values ('EE170828',0,'ABC656362-B21CBA')
insert into OrderReturn values ('EE170828',0,'ABC661069-B21#0D1CBA')
insert into OrderReturn values ('EE170828',0,'ABC654764-B21CBA')
insert into OrderReturn values ('EE170828',0,'ABC647893-B21#0D1CBA')
insert into OrderReturn values ('EE170828',0,'ABC661069-B21#0D1CBA')
insert into OrderReturn values ('EE170828',0,'ABC656362-B21#0D1CBA')
insert into OrderReturn values ('EE170828',0,'ABC652564-B21#0D1CBA')
insert into OrderReturn values ('EE170828',0,'ABC656362-B21#0D1CBA')
insert into OrderReturn values ('EE170828',0,'ABC652564-B21#0D1CBA')
insert into OrderReturn values ('EE170828',0,'ABC654081-B21#B19CBA')
insert into OrderReturn values ('EE170828',0,'ABC734807-B21#0D1CBA')
insert into OrderReturn values ('EE170828',0,'ABC654780-L21CBA')
insert into OrderReturn values ('EE170828',0,'ABC652564-B21#0D1CBA')
insert into OrderReturn values ('EE170828',0,'ABC734807-B21#0D1CBA')
insert into OrderReturn values ('EE170828',0,'ABC734807-B21#0D1CBA')
insert into OrderReturn values ('EE170828',0,'ABC654081-B21CBA')
insert into OrderReturn values ('EE170828',0,'ABC684208-B21CBA')
insert into OrderReturn values ('EE170828',0,'ABC656362-B21CBA')
insert into OrderReturn values ('EE170828',0,'ABC654764-L21CBA')
insert into OrderReturn values ('EE170828',0,'ABC684208-B21CBA')
insert into OrderReturn values ('EE170828',0,'ABC654764-B21#0D1CBA')
insert into OrderReturn values ('EE170828',0,'ABCAP770BCBA')
insert into OrderReturn values ('EE170828',0,'ABC684208-B21CBA')
insert into OrderReturn values ('EE170828',0,'ABCAP770B#0D1CBA')
insert into OrderReturn values ('EE170828',0,'ABC654081-B21CBA')
I want to update the field "orderLine" on the table "OrderReturn" from the values that are held in the table "Main". The join to each table is OrderID and mpn, but the table Main can have the same mpn appearing more than once.
I think cursor is required, so once it updates the orderLine for one of he mpn's it will then need to find the next available OrderLine to use for the same mpn.
Any ideas?
Thanks

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Dwain Camps SSC Guru Points: 86948 More actions · Answer 1

A CURSOR is probably not required.

I'm not sure what exactly you want to do when there are duplicates, but try this and see if it gives you what you're looking for:

UPDATE OrderReturn

SET orderLine=

(

SELECT TOP 1 orderLine

FROM Main

WHERE OrderReturn.OrderID = Main.OrderID AND OrderReturn.mpn = Main.mpn

);

SELECT *

FROM OrderReturn

ORDER BY orderLine;

My mantra: No loops! No CURSORs! No RBAR! Hoo-uh![/I]
My thought question: Have you ever been told that your query runs too fast?

My advice:
INDEXing a poor-performing query is like putting sugar on cat food. Yeah, it probably tastes better but are you sure you want to eat it?
The path of least resistance can be a slippery slope. Take care that fixing your fixes of fixes doesn't snowball and end up costing you more than fixing the root cause would have in the first place.

Need to UNPIVOT? Why not CROSS APPLY VALUES instead?[/url]
Since random numbers are too important to be left to chance, let's generate some![/url]
Learn to understand recursive CTEs by example.[/url]
[url url=http://www.sqlservercentral.com/articles/St

ChrisM@Work SSC Guru Points: 186127 More actions · Answer 2

There's an alternate interpretation of the question: the first match between the two tables (on OrderID, mpn) takes the first line number, the second match takes the second number and so on. All this requires is surrogate row numbering of OrderID, mpn partitions in both tables:

WITH

NumberedMain AS (

SELECT

OrderID, OrderLine, mpn,

rn = ROW_NUMBER() OVER(PARTITION BY OrderID, mpn ORDER BY OrderLine)

FROM Main

),

NumberedOrderReturn AS (

SELECT

OrderID, OrderLine, mpn,

rn = ROW_NUMBER() OVER(PARTITION BY OrderID, mpn ORDER BY OrderLine)

FROM OrderReturn

)

UPDATE r SET

OrderLine = m.OrderLine

FROM NumberedOrderReturn r

INNER JOIN NumberedMain m

ON m.OrderID = r.OrderID

AND m.mpn = r.mpn

AND m.rn = r.rn

^{“Write the query the simplest way. If through testing it becomes clear that the performance is inadequate, consider alternative query forms.” - Gail Shaw}

For fast, accurate and documented assistance in answering your questions, please read this article.
Understanding and using APPLY, (I) and (II) Paul White
Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden