title: Add or subtract time from datetime in SQL server
body: <p>I have a column offset in db as <code>varchar(50)</code> which contains a value such as <code>05:30:00</code> or <code>-2:15:00</code>.</p>
  
  <p>I need to add or subtract this value from another column which is a <code>DATETIME</code> datatype as <code>2011-07-22 14:51:00</code>.</p>