title: In SQL need to extract values from 2 columns containing NULL values
body: <p>I am extracting records from a table and the condition is </p>
  
  <p>(status_code is not in 'A') or (status_code is not in 'C' and SNbr is not in '01','02','03)</p>
  
  <p>Both the columns can have duplicate values and can contain NULL values. </p>
  
  <p>Here is the table data</p>
  
  <pre><code>status_code              SNbr
  A                        01
  A                        NULL
  A                        04 
  NULL                     NULL
  NULL                     01
  C                        NULL
  C                        01
  C                        04
  B                        01
  B                        NULL
  </code></pre>
  
  <p>Required O/P is </p>
  
  <pre><code>status_code              SNbr
  NULL                     NULL
  NULL                     01
  C                        NULL
  C                        04
  B                        01
  B                        NULL
  </code></pre>
  
  <p>Thanks in advance for your help</p>