title: How to find people in a database who live in the same cities?
body: <p>I'm new to SQL, and I'm asking for help in an apparently easy question, but it gets cumbersome in my mind.</p>
  
  <p>I have the following table:</p>
  
  <pre><code>ID   NAME   CITY
  ---------------------
  1    John   new york
  2    Sam    new york
  3    Tom    boston
  4    Bob    boston
  5    Jan    chicago
  6    Ted    san francisco
  7    Kat    boston
  </code></pre>
  
  <p>I want a query that returns all the people who live in a city that another person registered in the database also lives in. </p>
  
  <p>The answer, for the table I showed above, would be:</p>
  
  <pre><code>ID   NAME   CITY
  ---------------------
  1    John   new york
  2    Sam    new york
  3    Tom    boston
  4    Bob    boston
  7    Kat    boston
  </code></pre>