Problem med alter og opdater derefter i try catch med tran ved hjælp af Transact-SQL

Selvom jeg skriver mit eget svar - al ære går til @Mikael Eriksson, som foreslog, at jeg skulle adskille forskellige batches med en GO - så koden, der ændrer tabellen, ikke kommer i konflikt med kode, der bruger den ændrede tabel. Tak 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