title: how to add columns to existing hive external table?
body: <pre><code>create external table demotable(
  column1 string,
  column2 string,
  column3 string)
  row format delimited fields terminated by '|' 
  location '/data/demotable';
  </code></pre>
  
  <p>I create external table 'demotable' and the data in '/data/demotable' is like </p>
  
  <pre><code>aaa|bbb|ccc
  ddd|eee|fff
  www|ttt|uuu
  ...
  yyy|uuu|kkk
  </code></pre>
  
  <p>Now I want to add two more columns in my data and it is going to be like </p>
  
  <pre><code>aaa|bbb|ccc
  ddd|eee|fff
  www|ttt|uuu
  ...
  yyy|uuu|kkk|ppp|lll
  vvv|mmm|zzz|ttt|hhh
  </code></pre>
  
  <p>Is there any way to :</p>
  
  <p>1.add new columns in my table(for new data)</p>
  
  <p>2.keep the old data(just mark the last two columns as 'NULL') ?</p>