update1

1delete sc
2change args to left right
3annotation limit less than 100 charactors

Author: YanjieGao

sql/core/src/main/scala/org/apache/spark/sql/execution/basicOperators.scala

@@ -206,15 +206,16 @@ case class ExistingRdd(output: Seq[Attribute], rdd: RDD[Row]) extends LeafNode {
 
 /**
  * :: DeveloperApi ::
- * This operator support the substract function .Return an table with the elements from `this` that are not in `other`.
+ * This operator support the substract function .
+ * Return an table with the elements from `this` that are not in `other`.
  */
 @DeveloperApi
-case class Except(children: Seq[SparkPlan])(@transient sc: SparkContext) extends SparkPlan {
+case class Subtract(left:SparkPlan,right:SparkPlan) extends SparkPlan {
   // TODO:The input children:Seq[SparkPlan]  should only contain two SparkPlan
   override def output = children.head.output
 
   override def execute() = {
-    children(0).execute().subtract(children(1).execute())
+    left.execute().subtract(right.execute())
   }
 
   override def otherCopyArgs = sc :: Nil