title: Python Pandas Dataframe merge and pick only few columns
body: <p>I have a basic question on dataframe merge. After I merge two dataframe , is there a way to pick only few columns in the result. </p>
  
  <p>Taking an example from documentation </p>
  
  <p><a href="https://pandas.pydata.org/pandas-docs/stable/merging.html#" rel="noreferrer">https://pandas.pydata.org/pandas-docs/stable/merging.html#</a></p>
  
  <pre><code>left = pd.DataFrame({'key1': ['K0', 'K0', 'K1', 'K2'],
                      'key2': ['K0', 'K1', 'K0', 'K1'],
                       'A': ['A0', 'A1', 'A2', 'A3'],
                       'B': ['B0', 'B1', 'B2', 'B3']})
  
  
  right = pd.DataFrame({'key1': ['K0', 'K1', 'K1', 'K2'],
                            'key2': ['K0', 'K0', 'K0', 'K0'],
                            'C': ['C0', 'C1', 'C2', 'C3'],
                            'D': ['D0', 'D1', 'D2', 'D3']})
  
  
  
  result = pd.merge(left, right, on=['key1', 'key2'])
  </code></pre>
  
  <p>Result comes as : </p>
  
  <pre><code>    A   B key1 key2   C   D
  0  A0  B0   K0   K0  C0  D0
  1  A2  B2   K1   K0  C1  D1
  2  A2  B2   K1   K0  C2  D2
  None
  </code></pre>
  
  <p>Is there a way I can chose only column 'C' from 'right' dataframe? For example, I would like my result to be like:</p>
  
  <pre><code>    A   B key1 key2   C  
  0  A0  B0   K0   K0  C0  
  1  A2  B2   K1   K0  C1  
  2  A2  B2   K1   K0  C2  
  None
  </code></pre>