title: Case statement gives group by clause error
body: <p>The following query: </p>
  
  <pre><code>SELECT 
      CASE WHEN is_dog = 1 THEN COUNT(*) END AS dogs,
      CASE WHEN is_cats = 1 THEN count(*) END as cats
  FROM 
      animals
  WHERE
      birth_date &gt;= '2018-01-01';
  </code></pre>
  
  <p>I get this error:</p>
  
  <blockquote>
    <p>Invalid operation: column "is_dog" must appear in the GROUP BY clause or be used in an aggregate function</p>
  </blockquote>
  
  <p>What do I need to change on this? I'm new to using redshift.</p>