BTW, in a sequence like this, I cannot use the GO approach to make this work. Do you know what would be the best approach to have this entire script to execute ok?

IF NOT EXISTS (SELECT * FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = 'Advertis' AND COLUMN_NAME = 'AddUser')
   BEGIN
      ALTER TABLE [Advertis] ADD [AddUser] int
   END
   ELSE
   BEGIN
      ALTER TABLE [Advertis] ADD [AddUserTemporary] int
      UPDATE [Advertis] SET [AddUserTemporary]=AddUser
      ALTER TABLE [Advertis] DROP COLUMN [AddUser]
      EXEC sp_RENAME 'Advertis.AddUser-Temporary', 'AddUser' , 'COLUMN'
   END