title: Joining DataFrames in Julia
body: <p>I am using v7.0 of DataFrames.jl and was wondering if the is a way to join two <code>DataFrame</code>s such that all columns that the two <code>DataFrame</code>s share in common are joined together while columns not common between both <code>DataFrame</code>s are labeled as missing.</p>
  
  <p>The <code>join()</code> function seems create a new key for the <code>DataFrame</code>. 
  The <code>vcat</code> function seems to not be able to concatenate <code>DataFrame</code>s without the exact same column names. </p>
  
  <p>An example of what I meant below.</p>
  
  <p>I want to combine</p>
  
  <pre><code>df1 = DataFrame(
      A = [1, 1000, 10000, 100000],
      B = [1,2,3,4],
      D = ["N", "M", "I", "J"])
  df2 = DataFrame(
      A = [1,2],
      B = repeat(1:2, inner=1),
      C = ["hi","CE"])
  </code></pre>
  
  <p>in a way such that I get</p>
  
  <pre><code>df3 = DataFrame(
      A = [1,1000,10000,100000, 2],
      B = [1,2,3,4,2],
      C = ["hi", missing, missing, missing, "CE"],
      D = ["N", "M", "I", "J", missing]) 
  </code></pre>
  
  <p>I want to do this with large <code>DataFrame</code>s so adding keys isn't feasible manually.</p>