title: db2 query condition where column not in () while the column value is null
body: <p>Good day,</p>
  
  <p>I have a row of data with a column, call status, the value inside is null.</p>
  
  <p>If I query <code>select * from table where status not in ('EXP')</code>, before I run this query, I thought I can select the row of data because <code>status=null</code>, consider <code>not in ('EXP')</code> also. After I tried, I found that I cant query out this row of data. Wish to know why this happen.</p>
  
  <p>Try to Google it but maybe my question is not correct so I cant get correct search result from Google.</p>
  
  <p>Kindly advise.</p>