title: AFTER keyword in mysql ALTER table query
body: <p>I was browsing some code when I saw alter queries of the form:</p>
  
  <pre><code>alter table table_name add column tags varchar(25) default null after some_field;
  </code></pre>
  
  <p>Reading up on the <a href="http://dev.mysql.com/doc/refman/5.1/en/alter-table.html" rel="nofollow">mysql docs for <code>ALTER</code> Table</a>, the purpose of the AFTER keyword is</p>
  
  <blockquote>
    <p>To add a column at a specific position within a table row, use FIRST or AFTER col_name. The default is to add the column last. You can also use FIRST and AFTER in CHANGE or MODIFY operations to reorder columns within a table. </p>
  </blockquote>
  
  <p>When should one use this keyword, and would it be advisable to run it frequently to alter tables which have large number(millions) of rows?</p>