title: SQL find non-null columns
body: <p>I have a table of time-series data of which I need to find all columns that contain at least one non-null value within a given time period. So far I am using the following query:</p>
  
  <pre><code>select max(field1),max(field2),max(field3),... 
     from series where t_stamp between x and y
  </code></pre>
  
  <p>Afterwards I check each field of the result if it contains a non-null value. </p>
  
  <p>The table has around 70 columns and a time period can contain >100k entries.</p>
  
  <p>I wonder if there if there is a faster way to do this (using only standard sql). </p>
  
  <p>EDIT:
  Unfortunately, refactoring the table design is not an option for me.</p>