title: Pandas join on columns with different names
body: <p>I have two different data frames that I want to perform some sql operations on. Unfortunately, as is the case with the data I'm working with, the spelling is often different.   </p>
  
  <p>See the below as an example with what I thought the syntax would look like where userid belongs to df1 and username belongs to df2.  Anyone help me out?  </p>
  
  <pre><code> # not working - I assume some syntax issue?
  pd.merge(df1, df2, on = [['userid'=='username', 'column1']], how = 'left')
  </code></pre>