title: Merging two parquet files with different schemas
body: <p>I have two parquet files, Parquet A has 137 columns and Parquet B has 110 columns. Parquet A file has the entire history of the table. So Parquet A has all the fields for the entire history of the table. Parquet B is all the values today I pull in and 17 columns were deleted. I want to union parquet A with parquet B but they don't have the same amount of columns. So that fails everytime.</p>
  
  <p>I have tried mergeSchema but that fails. Is it possible to add the missing columns to parquet B and add nulls. Then make the union?</p>