update SparkStrategies.scala on master branch

[SPARK-2234][SQL]Spark SQL basicOperators add Except operator #1151

Author: YanjieGao

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

@@ -182,6 +182,8 @@ private[sql] abstract class SparkStrategies extends QueryPlanner[SparkPlan] {
         execution.Limit(limit, planLater(child))(sparkContext) :: Nil
       case Unions(unionChildren) =>
         execution.Union(unionChildren.map(planLater))(sparkContext) :: Nil
+      case logical.Except(left,right) =>                                        
+        execution.Subtract(planLater(left),planLater(right)) :: Nil 
       case logical.Generate(generator, join, outer, _, child) =>
         execution.Generate(generator, join = join, outer = outer, planLater(child)) :: Nil
       case logical.NoRelation =>