title: How to use Coalesce in MySQL
body: <p>A little help here. I really don't understand how to use this coalesce in MySQL</p>
  
  <p>I have read all the pages in page 1 result of <code>how to use coalsece</code> in google result. </p>
  
  <p>I know its meaning that it returns the first non-null value it encounters and null otherwise.</p>
  
  <p>But it's still vague for me.</p>
  
  <ol>
  <li>How come I saw queries that returns multiple values? Isn't it only the first not null value that is returned?</li>
  <li>And how do it decide which column to base? <code>coalesce(column1,column2)</code>? what if first column is null and other column is not null?</li>
  <li>Or if I'm wrong or my syntax is wrong, how do i properly write it?</li>
  <li>Can someone provide a very good and simple example on how to use it?</li>
  <li>And when it is desirable to use.</li>
  </ol>