title: SQL - HINT to reference a column
body: <p>I am very beginner at SQL, so I am sorry if this question is primitive. <br>
  I just started following the tutorial of <a href="http://www.w3schools.com" rel="noreferrer">http://www.w3schools.com</a>, so downloaded the "Northwind" database to try working on it, and using the pgAdmin 3 console to access the DB. 
  I just tried simple command to choose one column of the table, but it gives the same following message with any column from any table</p>
  
  <pre><code>LINE 1: select City from Customers;
                          ^
  HINT:  Perhaps you meant to reference the column "customers.City".
  </code></pre>
  
  <p>I would like to ask is there any thing wrong in my command? and how to fix it?</p>
  
  <p>Thanks</p>