title: how can we merge two dataframe without losing any row in python
body: <p>I have two dataframe as below.</p>
  
  <p>df1:</p>
  
  <pre><code>Student_Name,total
  X,400
  Y,350
  D,450
  E,420
  </code></pre>
  
  <p>df2:</p>
  
  <pre><code>Student_Name,jan
  X,350               
  Y,380
  A,360
  B,370
  Y,380
  </code></pre>
  
  <p>output:</p>
  
  <pre><code>Student_Name,jan,feb
  X,350,400               
  Y,380,350
  A,360,0
  B,370,0
  Y,380,350
  </code></pre>
  
  <p>output should have no. of row from df2, and value taken from df1. if df2 row label not found in df1 then there should be 0. also if df2 index column have duplicate . for example here Y is two times and both times we taken value for it from df1. also output should not have row which is not in df2 but in df1. here D and E is in df1 but not in df2 so don't include in output dataframe.</p>