title: Join two DataFrames on one key column / ERROR: 'columns overlap but no suffix specified'
body: <p>I have two tables: sales table &amp; product table and these two tables share the 'PART NUMBER' column.
  The 'PART NUMBER' column in the sales table is not unique, but it is unique in the product table. (see image below of a snapshot of the sales table &amp; product table)</p>
  
  <p><img src="https://i.stack.imgur.com/S1t7w.png" alt="enter image description here"></p>
  
  <p><img src="https://i.stack.imgur.com/qb9lL.png" alt="enter image description here"></p>
  
  <p>I was trying to add the equivalent 'Description' to each 'PART NUMBER' on the sales table, and I followed the <a href="http://pandas.pydata.org/pandas-docs/stable/merging.html#joining-key-columns-on-an-index" rel="noreferrer">examples</a> from the pandas website
  my code</p>
  
  <pre><code>sales.join(part_table, on='PART NUMBER')
  </code></pre>
  
  <p>But I got this error: </p>
  
  <pre><code>ValueError: columns overlap but no suffix specified: Index([u'PART NUMBER'], dtype='object')
  </code></pre>
  
  <p>Can someone explain what this error means and how to solve it?</p>
  
  <p>Many thanks!</p>