title: Hive: Difference between NULL col_name and NULL as col_name in table DDL
body: <p>Can someone please explain me the difference between "NULL col_name" and "NULL as col_name" in hive table DDL. Examples below:</p>
  
  <p>CREATE TABLE table_null AS
    SELECT c1, c2, c3, c4 FROM(
      'col1' as c1,
      'col2' as c2,
       NULL as c3,
       NULL c4 ......</p>