Github user chutium commented on a diff in the pull request:
https://github.com/apache/spark/pull/1612#discussion_r16704875
--- Diff: core/src/main/scala/org/apache/spark/rdd/JdbcRDD.scala ---
@@ -57,6 +61,8 @@ class JdbcRDD[T: ClassTag](
mapRow: (ResultSet) => T = JdbcRDD.resultSetToObjectArray _)
extends RDD[T](sc, Nil) with Logging {
+ private var schema: Seq[(String, Int, Boolean)] = null
--- End diff --
yep, i tried to do like you said before, but there is no public method or
attribute to get ResultSet or Statement from this ```JdbcRDD``` in spark core,
so in ```JdbcResultSetRDD``` i have no idea how can we get the metadata from
```JdbcRDD```... otherwise we do something like ```jdbcRDD.head``` then we can
get the metadata from first row, but it may execute the whole query at plan
phase.
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