Which one is the first priority between DDL and DML in sql server?

Hi,

       While executing the following scripts at one shot, I'm getting error message that is "Invalid column Name 'Subject'." May I know why this happened? Is there any priority between DDL and DML in sql server? Please any one let me know your thought (with example if possible).

SCRIPT:
       Alter table #TableName
            Add subject varchar(max)

      Update #TableName set subject= NULL

Thanks! in advance.