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]
GO

	DECLARE @TV bit
	DECLARE @EV bit
	
	    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])

UPDATE

        [DB2].[dbo].[Client]

    SET

        [FIELD1] =

        (

            CASE

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

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

				ELSE -1002

            END

        )

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