Github user HyukjinKwon commented on a diff in the pull request:
https://github.com/apache/spark/pull/12601#discussion_r69267347
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/jdbc/JDBCRelation.scala
---
@@ -96,7 +97,16 @@ private[sql] case class JDBCRelation(
override val needConversion: Boolean = false
- override val schema: StructType = JDBCRDD.resolveTable(url, table,
properties)
+ override val schema: StructType = {
+ val resolvedSchema = JDBCRDD.resolveTable(url, table, properties)
+ providedSchemaOption match {
+ case Some(providedSchema) =>
+ if (providedSchema.sql.toLowerCase ==
resolvedSchema.sql.toLowerCase) resolvedSchema
--- End diff --
I think `JDBCRDD.resolveTable` needs another query execution. Although it
would be less expensive than inferring schemas in CSV or JSON, it would be
still a bit of overhead. I am not 100% about this too. So, I think it might be
better to be consistent with the others in this case.
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