From 339b237dc18d4367b0735236b4b8be2901fcad79 Mon Sep 17 00:00:00 2001
From: Juliusz Sompolski <julek@databricks.com>
Date: Thu, 16 Mar 2017 08:20:47 +0800
Subject: [PATCH] [SPARK-19948] Document that saveAsTable uses catalog as
source of truth for table existence.
It is quirky behaviour that saveAsTable to e.g. a JDBC source with SaveMode other
than Overwrite will nevertheless overwrite the table in the external source,
if that table was not a catalog table.
Author: Juliusz Sompolski <julek@databricks.com>
Closes #17289 from juliuszsompolski/saveAsTableDoc.
---
.../main/scala/org/apache/spark/sql/DataFrameWriter.scala | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/DataFrameWriter.scala b/sql/core/src/main/scala/org/apache/spark/sql/DataFrameWriter.scala
index deaa800694..3e975ef6a3 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/DataFrameWriter.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/DataFrameWriter.scala
@@ -337,6 +337,11 @@ final class DataFrameWriter[T] private[sql](ds: Dataset[T]) {
* +---+---+
* }}}
*
+ * In this method, save mode is used to determine the behavior if the data source table exists in
+ * Spark catalog. We will always overwrite the underlying data of data source (e.g. a table in
+ * JDBC data source) if the table doesn't exist in Spark catalog, and will always append to the
+ * underlying data of data source if the table already exists.
+ *
* When the DataFrame is created from a non-partitioned `HadoopFsRelation` with a single input
* path, and the data source provider can be mapped to an existing Hive builtin SerDe (i.e. ORC
* and Parquet), the table is persisted in a Hive compatible format, which means other systems
--
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