title: Query error with 2 ambiguous column names in SQL
body: <p>I've been working with this Query for bit now and I'm having a hard time. I'm new to SQL and I can't figure our why I'm getting the error:</p>
  
  <pre><code>SELECT customer_number, first_name_initial, last_name,serve_address_1, serve_address_2, serve_city, serve_state, route_serve_zip_code, phone_number1, referral_code
  FROM customer_master 
  INNER JOIN route_detail 
  ON m.customer_number=r.customer_number
  WHERE (referral_code='american')
  </code></pre>
  
  <p>ERROR</p>
  
  <p>Msg 209, Level 16, State 1, Line 1
  Ambiguous column name 'customer_number'.
  Msg 209, Level 16, State 1, Line 1
  Ambiguous column name 'phone_number1'.</p>
  
  <p>I've tried appending the columns as follows but no luck with that either. Any help would be greatly appreciated!</p>
  
  <pre><code>SELECT customer_number, first_name_initial, last_name,serve_address_1, serve_address_2, serve_city, serve_state, route_serve_zip_code, phone_number1, referral_code
  FROM customer_master m
  INNER JOIN route_detail r
  ON m.customer_number=r.customer_number
  WHERE (referral_code='american')
  </code></pre>