Update multiple lines with CASE statement

I have a table with, say 1000 clients in it. I need to update a field in my table for each client with a different flag based on a mix of field values from a view that is in another database. The value will be different for each client in the table.

I am using the syntax below but I am missing something - any help greatly appreciated.

 USE [DB2]

	    SET @TV = (SELECT [Test1] FROM [DB1].[dbo].[vwClientTable] WHERE [DB1].[dbo].[vwClientTable].[MainID1] = [DB2].[dbo].[ClientTable].[MainID])
        SET @EV = (SELECT [Test2] FROM [DB1].[dbo].[vwClientTable] WHERE [DB1].[dbo].[vwClientTable].[MainID1] = [DB2].[dbo].[ClientTable].[MainID])




        [FIELD1] =



                WHEN @TV = 1 AND @EV = 1 THEN -1003

                WHEN @TV = 1 AND @EV = 0 THEN -1001

				ELSE -1002



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Arifhusen AnsariBusiness Intelligence Developer and AnalystCommented:

I am not sure about your script whether it was executed or not. You might get error in the first line it self.

You can go with below approach.

While updating multiple records in table.
I would suggest not to execute update query directly rather you can execute select query first and just verify whether you are getting data as per expectation or not. If everything goes well, you can covert that select query to update query.

Now let's come to your case. You need to update column in Client table based on data in two columns test1 and test2 in vwClientTable.

We will first build select query based on requirement and then convert it to update.

Using below query you can find whether you are getting correct value for your case statement or not.
Verify the same for some samples.

		WHEN t2.[Test1]=1 AND t2.Test2=1 THEN -1003
		WHEN t2.[Test1]=1 AND t2.Test2=0 THEN -1001
		ELSE -1002
	END as ValueTOUpdate

FROM [DB2].[dbo].[Client] t1 
INNER JOIN [DB1].[dbo].[vwClientTable] t2
ON t1.[MainID1]=t2.MainID

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If it looks great just convert select query to update one as below.

		WHEN t2.[Test1]=1 AND t2.Test2=1 THEN -1003
		WHEN t2.[Test1]=1 AND t2.Test2=0 THEN -1001
		ELSE -1002
FROM [DB2].[dbo].[Client] t1 
INNER JOIN [DB1].[dbo].[vwClientTable] t2
ON t1.[MainID1]=t2.MainID

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Hope it will help you and guide you when you do multiple updates.

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alexkingAuthor Commented:
That makes much more sense now - thank you so much :)
alexkingAuthor Commented:
Thank you very much - that was really helpful and I get it now :)
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Query Syntax

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