title: How can I inexpensively determine if a column contains only NULL records?
body: <p>I have a large table with 500 columns and 100M rows. Based on a small sample, I believe only about 50 of the columns contain any values, and the other 450 contain only NULL values. I want to list the columns that contain no data.</p>
  
  <p>On my current hardware, it would take about 24 hours to query every column (<code>select count(1) from tab where col_n is not null</code>)</p>
  
  <p>Is there a less expensive way to determine that a column is completely empty/NULL?</p>