Major Description
Spark SQL includes a data source that can read data from other databases using JDBC.
Spark also supports the case-insensitive option pushDownPredicate.
According to http://spark.apache.org/docs/latest/sql-data-sources-jdbc.html, If set pushDownPredicate to false, no filter will be pushed down to the JDBC data source and thus all filters will be handled by Spark.
But I find it still be pushed down to JDBC data source.
