title: change the size of datatype in sql
body: <p>I have created a table with column <code>id</code> as <code>varchar2(20)</code>. Now I want to modify it and change size to 13 i.e column <code>id varchar2(13)</code>. How to achieve it? Thanks in  advance</p>
  
  <p>p.s.: I don`t have any data in my table.</p>