title: SQL: Select rows with a column value that occurs at least N times?
body: <p>Suppose I have a SQL table "Celebrities" with two columns: "fname" and "lname":</p>
  
  <pre><code>fname    | lname    
  ---------+-------  
  Bill     | Clinton
  Bill     | Gates
  George   | Bush
  George   | Clinton
  Barack   | Obama
  </code></pre>
  
  <p>I would like to write a query that returns the first and last name of each person in the table whose last name appears at least twice in the column "lname".  How do I write this SQL query?</p>