title: When to pay attention to NULL values in SQL queries?
body: <p>I know that you should not use the clause <code>NOT IN</code> when you have <code>NULL</code> values you're trying to compare to. Also, an arithmetic operation involving a <code>NULL</code> returns <code>NULL</code>.</p>
  
  <p>However in other situations <code>NULL</code> values don't cause issues, for instance, there is no problem with operations such as <code>MAX</code>, <code>MIN</code>…</p>
  
  <p>So, what are situations/operations where one should be aware of <code>NULL</code> values?</p>
  
  <p>Thank you!</p>