title: IFNULL() Equivalent in PostgreSQL
body: <p>I am working on a project of migrating from MySQL to PostgreSQL, some function can't works well in PostgreSQL like <code>IFNULL</code> function. Some tutorials say that in PostgreSQL we can use <code>NULLIF</code> to handle it. 
  When I try I get an issue "<code>argument of NOT must be type boolean, not type integer</code>". </p>
  
  <p>This is the simple SQL :</p>
  
  <pre><code>SELECT * FROM `tableA` WHERE not(nullif(columnA, 0));
  </code></pre>
  
  <p>How to solve it? Maybe some one can make an explain how can it works well. Thanks</p>