title: query to get the difference between total number of rows and distinct rows
body: <p>I'm new to SQL, wasn't able to write the correct SQL.
  Given a table STATION that holds data for five fields namely ID, CITY, STATE, NORTHERN LATITUDE and WESTERN LONGITUDE.</p>
  
  <pre><code>+-------------+------------+
  | Field       |   Type     |
  +-------------+------------+
  | ID          | INTEGER    |
  | CITY        | VARCHAR(21)|
  | STATE       | VARCHAR(2) |
  | LAT_N       | NUMERIC    |
  | LONG_W      | NUMERIC    |
  +-------------+------------+
  </code></pre>
  
  <p>Let <code>NUM</code> be the number of cities and <code>NUMunique</code> be the number of unique cities, then write a query to print the value of <code>NUM</code> - <code>NUMunique</code>.</p>
  
  <p>I tried: </p>
  
  <pre><code>select (count(CITY)- distinct count(CITY)) from STATION; 
  </code></pre>