title: Test hive schema compatibility
body: <p>I want to test if changing datatype for a schema is compatible or not.
  Eg:</p>
  <pre><code>df1=spark.createDataframe([],StringType())
  df2=spark.createDataframe([],IntegerType())
  </code></pre>
  <p>I know if the two dfs are written as parquet, I can use mergeschema functionality to test if the two dfs read together are compatible or not</p>
  <p>How can I find at dataframe/schema level if the schemas allow implicit conversion? Is it even possible?</p>