Github user yhuai commented on a diff in the pull request:
https://github.com/apache/spark/pull/9495#discussion_r44035882
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/jdbc/JdbcDialects.scala ---
@@ -315,3 +316,27 @@ case object DerbyDialect extends JdbcDialect {
}
+/**
+ * :: DeveloperApi ::
+ * Default Oracle dialect, mapping a nonspecific
+ * numeric type to a general decimal type.
+ * Solution by @cloud-fan and @bdolbeare (github.com)
+ */
+@DeveloperApi
+case object OracleDialect extends JdbcDialect {
+ override def canHandle(url: String): Boolean =
url.startsWith("jdbc:oracle")
+ override def getCatalystType(
+ sqlType: Int, typeName: String, size: Int, md: MetadataBuilder):
Option[DataType] = {
+ // Handle NUMBER fields that have no precision/scale in special way
+ // because JDBC ResultSetMetaData converts this to 0 procision and
-127 scale
+ if (sqlType == Types.NUMERIC && size == 0) {
+ // This is sub-optimal as we have to pick a precision/scale in
advance whereas the data
+ // in Oracle is allowed to have different precision/scale for each
value.
+ // This conversion works in our domain for now though we need a
more durable solution.
+ // Look into changing JDBCRDD (line 406):
--- End diff --
I think putting the line number at here is not a very robust way. Since we
already described the problem, we can simply explain our workaround at here.
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