title: Incrementing multi-column sequence in PostgreSQL
body: <p>Is there any built-in way (I mean, without need of triggers and/or functions) to have incrementing indexes per multiple columns?</p>
  
  <p>So after performing:</p>
  
  <pre><code>INSERT INTO "table"
      ("month", "desc")
      VALUES
      (1, 'One thing')
  ,   (1, 'Another thing')
  ,   (1, 'Last task of the month')
  ,   (2, 'Last task of the month')
  ,   (2, 'Last task of the month')
  ,   (3, 'First of third month')
  </code></pre>
  
  <p>My table would end up like this (note the "task" column):</p>
  
  <pre><code>month    task    desc
  1        1       One thing
  1        2       Another thing
  1        3       Last task of the month
  2        1       First of second month
  2        2       Second and last of second month
  3        1       First of third month
  </code></pre>