Github user yhuai commented on the pull request:
https://github.com/apache/spark/pull/999#issuecomment-45814468
http://yhuai.github.io/spark-sql-core/api/#org.apache.spark.sql.json.JsonTable
goes through how a user should use JsonTable.
Right now, a user can optionally sample the dataset for the process of
schema inferring. It is possible that the schema based on the sampled dataset
has missing fields and wrong data types. In this case, after the execution of
first user query, the user should call adjustSchema to see if the schema has
been updated. After the first execution, the JsonTable should have the complete
schema.
Also, it will be good that we can provide facilities to let users refine
the inferred schema.
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