title: TypeError: 'Column' object is not callable using WithColumn
body: <p>I would like append a new column on dataframe "df" from function <code>get_distance</code>:</p>
  
  <pre class="lang-py prettyprint-override"><code>def get_distance(x, y):
      dfDistPerc = hiveContext.sql("select column3 as column3, \
                                    from tab \
                                    where column1 = '" + x + "' \
                                    and column2 = " + y + " \
                                    limit 1")
  
      result = dfDistPerc.select("column3").take(1)
      return result
  
  df = df.withColumn(
      "distance",
      lit(get_distance(df["column1"], df["column2"]))
  )
  </code></pre>
  
  <p>But, I get this:</p>
  
  <pre><code>TypeError: 'Column' object is not callable
  </code></pre>
  
  <p>I think it happens because x and y are <code>Column</code> objects and I need to be converted to <code>String</code> to use in my query. Am I right? If so, how can I do this?</p>