[SPARK-5135][SQL] Add support for describe table to DDL in SQLContext

Hi, rxin marmbrus
I considered your suggestion (in #4127) and now re-write it. This is now up-to-date.
Could u please review it ?

Author: OopsOutOfMemory <victorshengli@126.com>

Closes #4227 from OopsOutOfMemory/describe and squashes the following commits:

053826f [OopsOutOfMemory] describe

5 files changed, 10 insertions, 21 deletions

diff --git a/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveContext.scala b/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveContext.scala
index 1921bf6e5e..d2371d4a55 100644
--- a/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveContext.scala
+++ b/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveContext.scala
@@ -75,7 +75,7 @@ class HiveContext(sc: SparkContext) extends SQLContext(sc) {
       DataFrame(this,
         ddlParser(sqlText, exceptionOnError = false).getOrElse(HiveQl.parseSql(substituted)))
     }  else {
-      sys.error(s"Unsupported SQL dialect: ${conf.dialect}.  Try 'sql' or 'hiveql'")
+      sys.error(s"Unsupported SQL dialect: ${conf.dialect}. Try 'sql' or 'hiveql'")
     }
   }
 
diff --git a/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveQl.scala b/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveQl.scala
index 62e9d92eac..c19a091719 100644
--- a/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveQl.scala
+++ b/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveQl.scala
@@ -34,6 +34,7 @@ import org.apache.spark.sql.catalyst.plans._
 import org.apache.spark.sql.catalyst.plans.logical
 import org.apache.spark.sql.catalyst.plans.logical._
 import org.apache.spark.sql.execution.ExplainCommand
+import org.apache.spark.sql.sources.DescribeCommand
 import org.apache.spark.sql.hive.execution.{HiveNativeCommand, DropTable, AnalyzeTable, HiveScriptIOSchema}
 import org.apache.spark.sql.types._
 
@@ -47,22 +48,6 @@ import scala.collection.JavaConversions._
  */
 private[hive] case object NativePlaceholder extends Command
 
-/**
- * Returned for the "DESCRIBE [EXTENDED] [dbName.]tableName" command.
- * @param table The table to be described.
- * @param isExtended True if "DESCRIBE EXTENDED" is used. Otherwise, false.
- *                   It is effective only when the table is a Hive table.
- */
-case class DescribeCommand(
-    table: LogicalPlan,
-    isExtended: Boolean) extends Command {
-  override def output = Seq(
-    // Column names are based on Hive.
-    AttributeReference("col_name", StringType, nullable = false)(),
-    AttributeReference("data_type", StringType, nullable = false)(),
-    AttributeReference("comment", StringType, nullable = false)())
-}
-
 /** Provides a mapping from HiveQL statements to catalyst logical plans and expression trees. */
 private[hive] object HiveQl {
   protected val nativeCommands = Seq(
diff --git a/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveStrategies.scala b/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveStrategies.scala
index d89111094b..7857a0252e 100644
--- a/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveStrategies.scala
+++ b/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveStrategies.scala
@@ -29,6 +29,7 @@ import org.apache.spark.sql.catalyst.expressions.codegen.GeneratePredicate
 import org.apache.spark.sql.catalyst.planning._
 import org.apache.spark.sql.catalyst.plans._
 import org.apache.spark.sql.catalyst.plans.logical.LogicalPlan
+import org.apache.spark.sql.sources.DescribeCommand
 import org.apache.spark.sql.execution.{DescribeCommand => RunnableDescribeCommand}
 import org.apache.spark.sql.execution._
 import org.apache.spark.sql.hive.execution._
@@ -240,8 +241,11 @@ private[hive] trait HiveStrategies {
           case t: MetastoreRelation =>
             ExecutedCommand(
               DescribeHiveTableCommand(t, describe.output, describe.isExtended)) :: Nil
+
           case o: LogicalPlan =>
-            ExecutedCommand(RunnableDescribeCommand(planLater(o), describe.output)) :: Nil
+            val resultPlan = context.executePlan(o).executedPlan
+            ExecutedCommand(RunnableDescribeCommand(
+              resultPlan, describe.output, describe.isExtended)) :: Nil
         }
 
       case _ => Nil
diff --git a/sql/hive/src/test/scala/org/apache/spark/sql/hive/execution/HiveComparisonTest.scala b/sql/hive/src/test/scala/org/apache/spark/sql/hive/execution/HiveComparisonTest.scala
index f8a957d55d..a90bd1e257 100644
--- a/sql/hive/src/test/scala/org/apache/spark/sql/hive/execution/HiveComparisonTest.scala
+++ b/sql/hive/src/test/scala/org/apache/spark/sql/hive/execution/HiveComparisonTest.scala
@@ -22,8 +22,8 @@ import java.io._
 import org.scalatest.{BeforeAndAfterAll, FunSuite, GivenWhenThen}
 
 import org.apache.spark.Logging
+import org.apache.spark.sql.sources.DescribeCommand
 import org.apache.spark.sql.execution.{SetCommand, ExplainCommand}
-import org.apache.spark.sql.hive.DescribeCommand
 import org.apache.spark.sql.catalyst.planning.PhysicalOperation
 import org.apache.spark.sql.catalyst.plans.logical._
 import org.apache.spark.sql.catalyst.util._
diff --git a/sql/hive/src/test/scala/org/apache/spark/sql/hive/execution/HiveQuerySuite.scala b/sql/hive/src/test/scala/org/apache/spark/sql/hive/execution/HiveQuerySuite.scala
index 407d6058c3..bb73ff1ea7 100644
--- a/sql/hive/src/test/scala/org/apache/spark/sql/hive/execution/HiveQuerySuite.scala
+++ b/sql/hive/src/test/scala/org/apache/spark/sql/hive/execution/HiveQuerySuite.scala
@@ -741,8 +741,8 @@ class HiveQuerySuite extends HiveComparisonTest with BeforeAndAfter {
 
     assertResult(
       Array(
-        Row("a", "IntegerType", null),
-        Row("b", "StringType", null))
+        Row("a", "int", ""),
+        Row("b", "string", ""))
     ) {
       sql("DESCRIBE test_describe_commands2")
         .select('col_name, 'data_type, 'comment)