title: Excel Date Formula
body: <p>I have 3 cells in Excel as follows:</p>
  
  <p>Cell   </p>
  
  <blockquote>
    <p>A1=2012<br>
      A2=12<br>
      A3=15</p>
  </blockquote>
  
  <p>Which contains year, month &amp; date value respectively. And I want to make a date string out of it.</p>
  
  <p>I know it's very easy to achieve using <code>Date</code> function. 
  But I also want the cell to remain blank if any of A1,A2 or A3 is blank.</p>