[SPARK-16734][EXAMPLES][SQL] Revise examples of all language bindings

## What changes were proposed in this pull request?

This PR makes various minor updates to examples of all language bindings to make sure they are consistent with each other. Some typos and missing parts (JDBC example in Scala/Java/Python) are also fixed.

## How was this patch tested?

Manually tested.

Author: Cheng Lian <lian@databricks.com>

Closes #14368 from liancheng/revise-examples.

2 files changed, 18 insertions, 7 deletions

diff --git a/examples/src/main/java/org/apache/spark/examples/sql/JavaSQLDataSourceExample.java b/examples/src/main/java/org/apache/spark/examples/sql/JavaSQLDataSourceExample.java
index ec02c8bbb8..52e3b62b79 100644
--- a/examples/src/main/java/org/apache/spark/examples/sql/JavaSQLDataSourceExample.java
+++ b/examples/src/main/java/org/apache/spark/examples/sql/JavaSQLDataSourceExample.java
@@ -25,7 +25,6 @@ import java.util.List;
 // $example on:basic_parquet_example$
 import org.apache.spark.api.java.function.MapFunction;
 import org.apache.spark.sql.Encoders;
-// import org.apache.spark.sql.Encoders;
 // $example on:schema_merging$
 // $example on:json_dataset$
 import org.apache.spark.sql.Dataset;
@@ -92,7 +91,7 @@ public class JavaSQLDataSourceExample {
   public static void main(String[] args) {
     SparkSession spark = SparkSession
       .builder()
-      .appName("Java Spark SQL Data Sources Example")
+      .appName("Java Spark SQL data sources example")
       .config("spark.some.config.option", "some-value")
       .getOrCreate();
 
@@ -100,6 +99,7 @@ public class JavaSQLDataSourceExample {
     runBasicParquetExample(spark);
     runParquetSchemaMergingExample(spark);
     runJsonDatasetExample(spark);
+    runJdbcDatasetExample(spark);
 
     spark.stop();
   }
@@ -183,10 +183,10 @@ public class JavaSQLDataSourceExample {
     // The final schema consists of all 3 columns in the Parquet files together
     // with the partitioning column appeared in the partition directory paths
     // root
-    // |-- value: int (nullable = true)
-    // |-- square: int (nullable = true)
-    // |-- cube: int (nullable = true)
-    // |-- key : int (nullable = true)
+    //  |-- value: int (nullable = true)
+    //  |-- square: int (nullable = true)
+    //  |-- cube: int (nullable = true)
+    //  |-- key: int (nullable = true)
     // $example off:schema_merging$
   }
 
@@ -216,4 +216,15 @@ public class JavaSQLDataSourceExample {
     // $example off:json_dataset$
   }
 
+  private static void runJdbcDatasetExample(SparkSession spark) {
+    // $example on:jdbc_dataset$
+    Dataset<Row> jdbcDF = spark.read()
+      .format("jdbc")
+      .option("url", "jdbc:postgresql:dbserver")
+      .option("dbtable", "schema.tablename")
+      .option("user", "username")
+      .option("password", "password")
+      .load();
+    // $example off:jdbc_dataset$
+  }
 }
diff --git a/examples/src/main/java/org/apache/spark/examples/sql/JavaSparkSQLExample.java b/examples/src/main/java/org/apache/spark/examples/sql/JavaSparkSQLExample.java
index afc18078d4..cff9032f52 100644
--- a/examples/src/main/java/org/apache/spark/examples/sql/JavaSparkSQLExample.java
+++ b/examples/src/main/java/org/apache/spark/examples/sql/JavaSparkSQLExample.java
@@ -88,7 +88,7 @@ public class JavaSparkSQLExample {
     // $example on:init_session$
     SparkSession spark = SparkSession
       .builder()
-      .appName("Java Spark SQL Example")
+      .appName("Java Spark SQL basic example")
       .config("spark.some.config.option", "some-value")
       .getOrCreate();
     // $example off:init_session$