Även om jag skriver mitt eget svar - all ära går till @Mikael Eriksson, som föreslog att jag måste separera olika batcher med en GO - så att koden som ändrar tabellen inte kommer i konflikt med kod som använder den ändrade tabellen. Tack Mikael!
USE PUK;
GO
BEGIN TRANSACTION;
BEGIN TRY
-- - Modify RETRIEVAL_STAT
alter table dbo.RETRIEVAL_STAT add
SOURCE nvarchar(10) NULL,
ACCOUNTNUMBER nvarchar(50) NULL,
PUK nvarchar(20) NULL;
END TRY
BEGIN CATCH
SELECT
ERROR_NUMBER() AS ErrorNumber
,ERROR_SEVERITY() AS ErrorSeverity
,ERROR_STATE() AS ErrorState
,ERROR_PROCEDURE() AS ErrorProcedure
,ERROR_LINE() AS ErrorLine
,ERROR_MESSAGE() AS ErrorMessage;
IF @@TRANCOUNT > 0
ROLLBACK TRANSACTION;
END CATCH;
IF @@TRANCOUNT > 0
COMMIT TRANSACTION;
GO
USE PUK;
GO
BEGIN TRANSACTION;
BEGIN TRY
-- transform logic.
UPDATE dbo.RETRIEVAL_STAT
SET SOURCE = 'ABC',
ACCOUNTNUMBER = ABC.ACCOUNTNUMBER,
PUK = ABC.PUK
FROM RETRIEVAL_STAT RS
INNER JOIN ABC
ON RS.SERVICE_NUMBER = ABC.SERVICENUMBER;
UPDATE dbo.RETRIEVAL_STAT
SET SOURCE = 'DEF',
ACCOUNTNUMBER = DEF.BILLINGACCOUNTNUMBER ,
PUK = DEF.PUK
FROM RETRIEVAL_STAT RS
INNER JOIN DEF
ON RS.SERVICE_NUMBER = DEF.SERVICENUMBER;
UPDATE dbo.RETRIEVAL_STAT
SET SOURCE = 'No Match'
WHERE SOURCE IS NULL;
-- Fix other columns that should be not nullable.
alter table dbo.RETRIEVAL_STAT
alter column SERVICE_NUMBER nvarchar (50) NOT NULL;
alter table dbo.DEF
alter column PUK nvarchar (20) NOT NULL;
END TRY
BEGIN CATCH
SELECT
ERROR_NUMBER() AS ErrorNumber
,ERROR_SEVERITY() AS ErrorSeverity
,ERROR_STATE() AS ErrorState
,ERROR_PROCEDURE() AS ErrorProcedure
,ERROR_LINE() AS ErrorLine
,ERROR_MESSAGE() AS ErrorMessage;
IF @@TRANCOUNT > 0
ROLLBACK TRANSACTION;
END CATCH;
IF @@TRANCOUNT > 0
COMMIT TRANSACTION;
GO