title: how to Update duplicate rows without primary key
body: <p>i have a table with NO Primary Key.</p>
  
  <pre><code>name      age       sex
  a         12        m
  b         61        m
  c         23        f
  d         12        m
  a         12        m
  a         12        m
  f         14        f
  </code></pre>
  
  <p>i have exactly 3 similar rows-row-1,row-5 and row-6.
  i want to update row-5 without affecting row-1 and row-6.
  Pls help me out, how to achieve this.</p>