title: How handle schema changes in glue and get the expected output in csv?
body: <p>I am trying to crawl some files having different sachems(Data compatible ) using AWS Glue.<br>
  As I read in the AWS documentation  that Glue crawlers update the catalog tables for any change in the schema(add new columns and remove missing columns). 
  I have checked the "Update the table definition in the Data Catalog"  and "Create a single schema for each S3 path" while creating the crawler.<br>
  Example:<br>
  let's say I have a file "File1.csv"  as shown below:</p>
  
  <p>name,age,loc</p>
  
  <p>Ravi,12,Ind</p>
  
  <p>Joe,32,US</p>
  
  <p>Say I have another file "File2.csv" as shown below:</p>
  
  <p>name,age,height</p>
  
  <p>Jack,12,160</p>
  
  <p>Jane,32,180</p>
  
  <p>After crawlers run in the schema was updated as:
  name,age,loc,height -This is as expcted
  but When I tried to read the files using Athena or tried writing the content of both the files to csv using Glue ETL job,I have observed that:
  the output looks like:</p>
  
  <p>name,age,loc,height</p>
  
  <p>Ravi,12,Ind,,</p>
  
  <p>Joe,32,US,,</p>
  
  <p>Jack,12,160,,</p>
  
  <p>Jane,32,180,,</p>
  
  <p>last two rows should have blank for loc as the second file didn't have loc column.</p>
  
  <p>where as expected:</p>
  
  <p>name,age,loc,height</p>
  
  <p>Ravi,12,Ind,,</p>
  
  <p>Joe,32,US,,</p>
  
  <p>Jack,12,,160</p>
  
  <p>Jane,32,,180</p>
  
  <p>In short glue is trying to fill up the column in contiguous manner in the combined output.Is there any way I can get the expected output?</p>