title: filter NULL values from query
body: <p>In the below query I want only to saw the rows that dont have NULL values in risk column</p>
  
  <pre><code>SELECT table1.id, table1.name,
     CASE 
       WHEN table1.event = 'r' AND table1.name = 'jones' THEN 'very high'
       WHEN table1.event = 't' AND table1.name = 'smith' THEN 'very low'
       ELSE (SELECT table2.risk FROM table2 WHERE table2.value &lt;= table1.value
             ORDER BY table2.value DESC LIMIT 1)
     END AS risk
  FROM table1
  ORDER BY FIELD( table1.event, 'r', 'f', 't' ), table1.value DESC
  </code></pre>
  
  <p>thanks.</p>
  
  <p><strong>The result of the above query is:</strong></p>
  
  <pre><code>id  name            risk
  17  name            very low
  17  name            NULL
  18  qwert yuiop very low
  18  qwert yuiop NULL
  19  qwert yuiop very low
  19  qwert yuiop NULL
  20  qwert yuiop very low
  20  qwert yuiop NULL
  21  qwert yuiop very low
  21  qwert yuiop NULL
  22  q           very low
  22  q           NULL
  23  q           very low
  23  q           NULL
  24  q           very low
  24  q           NULL
  25  q           very low
  25  q           NULL
  26  q           very low
  26  q           NULL
  </code></pre>
  
  <p>And I want to get rid of the NULL's.</p>