[SPARK-16387][SQL] JDBC Writer should use dialect to quote field names.

## What changes were proposed in this pull request?

Currently, JDBC Writer uses dialects to get datatypes, but doesn't to quote field names. This PR uses dialects to quote the field names, too.

**Reported Error Scenario (MySQL case)**
```scala
scala> val url="jdbc:mysql://localhost:3306/temp"
scala> val prop = new java.util.Properties
scala> prop.setProperty("user","root")
scala> spark.createDataset(Seq("a","b","c")).toDF("order")
scala> df.write.mode("overwrite").jdbc(url, "temptable", prop)
...MySQLSyntaxErrorException: ... near 'order TEXT )
```

## How was this patch tested?

Pass the Jenkins tests and manually do the above case.

Author: Dongjoon Hyun <dongjoon@apache.org>

Closes #14107 from dongjoon-hyun/SPARK-16387.

1 files changed, 6 insertions, 0 deletions

diff --git a/sql/core/src/test/scala/org/apache/spark/sql/jdbc/JDBCSuite.scala b/sql/core/src/test/scala/org/apache/spark/sql/jdbc/JDBCSuite.scala
index 11e66ad080..228e4250f3 100644
--- a/sql/core/src/test/scala/org/apache/spark/sql/jdbc/JDBCSuite.scala
+++ b/sql/core/src/test/scala/org/apache/spark/sql/jdbc/JDBCSuite.scala
@@ -764,4 +764,10 @@ class JDBCSuite extends SparkFunSuite
       assertEmptyQuery(s"SELECT * FROM tempFrame where $FALSE2")
     }
   }
+
+  test("SPARK-16387: Reserved SQL words are not escaped by JDBC writer") {
+    val df = spark.createDataset(Seq("a", "b", "c")).toDF("order")
+    val schema = JdbcUtils.schemaString(df, "jdbc:mysql://localhost:3306/temp")
+    assert(schema.contains("`order` TEXT"))
+  }
 }