Revert previous attempt

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/parser/CatalystQl.scala

@@ -201,7 +201,7 @@ https://cwiki.apache.org/confluence/display/Hive/Enhanced+Aggregation%2C+Cube%2C
 
           val relations = fromClause match {
             case Some(f) => nodeToRelation(f)
-            case None => OneRowRelation()
+            case None => OneRowRelation
           }
 
           val withLateralView = lateralViewClause.map { lv =>

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/basicOperators.scala

@@ -673,7 +673,7 @@ case class Repartition(numPartitions: Int, shuffle: Boolean, child: LogicalPlan)
 /**
  * A relation with one row. This is used in "SELECT ..." without a from clause.
  */
-case class OneRowRelation() extends LeafNode {
+case object OneRowRelation extends LeafNode {
   override def maxRows: Option[Long] = Some(1)
   override def output: Seq[Attribute] = Nil
 

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/ExpressionEvalHelper.scala

@@ -152,7 +152,7 @@ trait ExpressionEvalHelper extends GeneratorDrivenPropertyChecks {
       expression: Expression,
       expected: Any,
       inputRow: InternalRow = EmptyRow): Unit = {
-    val plan = Project(Alias(expression, s"Optimized($expression)")() :: Nil, OneRowRelation())
+    val plan = Project(Alias(expression, s"Optimized($expression)")() :: Nil, OneRowRelation)
     val optimizedPlan = DefaultOptimizer.execute(plan)
     checkEvaluationWithoutCodegen(optimizedPlan.expressions.head, expected, inputRow)
   }

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/MathFunctionsSuite.scala

@@ -150,7 +150,7 @@ class MathFunctionsSuite extends SparkFunSuite with ExpressionEvalHelper {
   private def checkNaNWithOptimization(
     expression: Expression,
     inputRow: InternalRow = EmptyRow): Unit = {
-    val plan = Project(Alias(expression, s"Optimized($expression)")() :: Nil, OneRowRelation())
+    val plan = Project(Alias(expression, s"Optimized($expression)")() :: Nil, OneRowRelation)
     val optimizedPlan = DefaultOptimizer.execute(plan)
     checkNaNWithoutCodegen(optimizedPlan.expressions.head, inputRow)
   }

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/ColumnPruningSuite.scala

@@ -160,7 +160,7 @@ class ColumnPruningSuite extends PlanTest {
   }
 
   test("Eliminate the Project with an empty projectList") {
-    val input = OneRowRelation()
+    val input = OneRowRelation
     val expected = Project(Literal(1).as("1") :: Nil, input).analyze
 
     val query1 =

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/EliminateSubqueryAliasesSuite.scala

@@ -35,8 +35,8 @@ class EliminateSubqueryAliasesSuite extends PlanTest with PredicateHelper {
   }
 
   private def assertEquivalent(e1: Expression, e2: Expression): Unit = {
-    val correctAnswer = Project(Alias(e2, "out")() :: Nil, OneRowRelation()).analyze
-    val actual = Optimize.execute(Project(Alias(e1, "out")() :: Nil, OneRowRelation()).analyze)
+    val correctAnswer = Project(Alias(e2, "out")() :: Nil, OneRowRelation).analyze
+    val actual = Optimize.execute(Project(Alias(e1, "out")() :: Nil, OneRowRelation).analyze)
     comparePlans(actual, correctAnswer)
   }
 

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/SimplifyConditionalSuite.scala

@@ -33,7 +33,7 @@ class SimplifyConditionalSuite extends PlanTest with PredicateHelper {
   }
 
   protected def assertEquivalent(e1: Expression, e2: Expression): Unit = {
-    val correctAnswer = Project(Alias(e2, "out")() :: Nil, OneRowRelation()).analyze
+    val correctAnswer = Project(Alias(e2, "out")() :: Nil, OneRowRelation).analyze
     val actual = Optimize.execute(Project(Alias(e1, "out")() :: Nil, OneRowRelation).analyze)
     comparePlans(actual, correctAnswer)
   }

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/parser/CatalystQlSuite.scala

@@ -29,7 +29,7 @@ class CatalystQlSuite extends PlanTest {
   val parser = new CatalystQl()
 
   test("test case insensitive") {
-    val result = Project(UnresolvedAlias(Literal(1)):: Nil, OneRowRelation())
+    val result = Project(UnresolvedAlias(Literal(1)):: Nil, OneRowRelation)
     assert(result === parser.parsePlan("seLect 1"))
     assert(result === parser.parsePlan("select 1"))
     assert(result === parser.parsePlan("SELECT 1"))
@@ -42,7 +42,7 @@ class CatalystQlSuite extends PlanTest {
         Not(
           GreaterThan(Literal(true), Literal(true)))
       ) :: Nil,
-      OneRowRelation())
+      OneRowRelation)
     comparePlans(parsed, expected)
   }
 
@@ -82,7 +82,7 @@ class CatalystQlSuite extends PlanTest {
         UnresolvedAlias(
           Literal(result)
         ) :: Nil,
-        OneRowRelation())
+        OneRowRelation)
       comparePlans(parsed, expected)
     }
 
@@ -133,7 +133,7 @@ class CatalystQlSuite extends PlanTest {
         UnresolvedAlias(
           Literal(output)
         ) :: Nil,
-        OneRowRelation())
+        OneRowRelation)
       comparePlans(parsed, expected)
     }
 

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/plans/PlanTest.scala

@@ -66,6 +66,6 @@ abstract class PlanTest extends SparkFunSuite with PredicateHelper {
 
   /** Fails the test if the two expressions do not match */
   protected def compareExpressions(e1: Expression, e2: Expression): Unit = {
-    comparePlans(Filter(e1, OneRowRelation()), Filter(e2, OneRowRelation()))
+    comparePlans(Filter(e1, OneRowRelation), Filter(e2, OneRowRelation))
   }
 }

sql/hive/src/main/scala/org/apache/spark/sql/hive/SQLBuilder.scala

@@ -481,14 +481,14 @@ class SQLBuilder(logicalPlan: LogicalPlan, sqlContext: SQLContext) extends Loggi
     }
 
     private def addSubqueryIfNeeded(plan: LogicalPlan): LogicalPlan = plan match {
-      case _: SubqueryAlias => plan
-      case _: Filter => plan
-      case _: Join => plan
-      case _: LocalLimit => plan
-      case _: GlobalLimit => plan
-      case _: SQLTable => plan
-      case _: Generate => plan
-      case _: OneRowRelation => plan
+      case _: SubqueryAlias |
+           _: Filter |
+           _: Join |
+           _: LocalLimit |
+           _: GlobalLimit |
+           _: SQLTable |
+           _: Generate |
+           OneRowRelation => plan
       case _ => addSubquery(plan)
     }
   }