Updates comments

Author: liancheng

sql/core/src/main/scala/org/apache/spark/sql/sources/commands.scala

@@ -96,7 +96,7 @@ private[sql] case class InsertIntoHadoopFsRelation(
       // We create a DataFrame by applying the schema of relation to the data to make sure.
       // We are writing data based on the expected schema,
       val df = {
-        // For partitioned relation r, r.schema's column ordering is different with the column
+        // For partitioned relation r, r.schema's column ordering can be different from the column
         // ordering of data.logicalPlan (partition columns are all moved after data column). We
         // need a Project to adjust the ordering, so that inside InsertIntoHadoopFsRelation, we can
         // safely apply the schema of r.schema to the data.

sql/core/src/main/scala/org/apache/spark/sql/sources/ddl.scala

@@ -322,6 +322,9 @@ private[sql] object ResolvedDataSource {
           Some(partitionColumnsSchema(data.schema, partitionColumns)),
           caseInsensitiveOptions)
 
+        // For partitioned relation r, r.schema's column ordering can be different from the column
+        // ordering of data.logicalPlan (partition columns are all moved after data column).  This
+        // will be adjusted within InsertIntoHadoopFsRelation.
         sqlContext.executePlan(
           InsertIntoHadoopFsRelation(
             r,