title: SQL if select statement returns no rows then perform alternative select statement
body: <p>Basically, what syntex would allow me to achieve the title statement?</p>
  
  <pre><code>If (select statement 1) returns 0 rows THEN (select statement 2) else (select statement 3)
  </code></pre>
  
  <p>So that the sql returns results from either statement 2 or 3
  I've looked for a way to do this but nothing I've found so far seems to exactly address the if requirements.</p>