title: Mysql Query for getting first instance of a element
body: <p>I have a table that has data like below(sorted by date)</p>
  
  <pre><code>COL_A | COL_B
  
  Item1 | Date1
  Item2 | Date1
  Item2 | Date2
  Item1 | Date3
  Item3 | Date3
  </code></pre>
  
  <p>Now I want a query that will return the first instance of every Item ie the result set should be like;</p>
  
  <pre><code>COL_A | COL_B
  
  Item1 | Date1
  Item2 | Date1
  Item3 | Date3
  </code></pre>
  
  <p>How to do this?</p>