title: Need to count unique observations for three variables taken together
body: <p>I have a data set of 5 million observations and three variables of interest are state codes, county codes and tract codes. Now I need to find the total count for distinct observations when taking three variables together. in general one can find a distinct count for a particular variable by:</p>
  
  <pre><code>PROC sql;
  SELECT COUNT(DISTINCT(TRACT)) 
      AS COUNT FROM metro1_00;
  quit;
  </code></pre>
  
  <p>But I need the unique count like (tract AND county AND state). but unfortunately such options are not available. I'm using SAS 9.3.</p>