title: MySQL : Concat in where clause not working
body: <p>I am facing a strange problem in mysql while searching multiple columns at once.</p>
  
  <p><code>select * from postal_address where concat(address1, ' ', address2) = 'ABC DEF';</code></p>
  
  <p>The above query returns data perfectly but the following doesn't return any data</p>
  
  <p><code>select * from postal_address where concat(address1, ' ', address2) != 'ABC DEF';</code></p>
  
  <p>I have other rows which have null values in the table for those columns. </p>