title: Single SQL query to tackle NULL and non-NULL values
body: <p>I have a stored procedure that has a parameter that can be either NULL or non-NULL value.
  I need to compare this parameter in the WHERE clause. If the parameter is non-NULL,</p>
  
  <pre><code>where ...
  and parameter = non-NULL-value
  </code></pre>
  
  <p>will work. </p>
  
  <p>But when the parameter will be null, it will not be ANSI-compliant:</p>
  
  <pre><code>where ...
  and parameter = NULL
  </code></pre>
  
  <p>I don't want to write two separate queries. How do I ensure ANSI-compliance in the same query?</p>