rxin's comments.

Author: yhuai

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

@@ -62,11 +62,7 @@ case class ExplainCommand(plan: LogicalPlan) extends Command {
 case class CacheCommand(tableName: String, doCache: Boolean) extends Command
 
 /**
- * Returned for the "DESCRIBE tableName" command.
- */
-
-/**
- * Returned for the "DESCRIBE tableName" 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.

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

@@ -403,6 +403,7 @@ private[hive] object HiveQl {
             nameParts.head match {
               case Token(".", dbName :: tableName :: Nil) =>
                 // It is describing a table with the format like "describe db.table".
+                // TODO: Actually, a user may mean tableName.columnName. Need to resolve this issue.
                 val (db, tableName) = extractDbNameTableName(nameParts.head)
                 DescribeCommand(
                   UnresolvedRelation(db, tableName, None), extended.isDefined)

sql/hive/src/test/scala/org/apache/spark/sql/hive/execution/HiveComparisonTest.scala

@@ -145,9 +145,11 @@ abstract class HiveComparisonTest
       case _: LogicalNativeCommand => answer.filterNot(nonDeterministicLine).filterNot(_ == "")
       case _: ExplainCommand => answer
       case _: DescribeCommand =>
+        // Filter out non-deterministic lines and lines which do not have actual results but
+        // can introduce problems because of the way Hive formats these lines.
+        // Then, remove empty lines. Do not sort the results.
         answer.filterNot(
-          r => nonDeterministicLine(r) || ignoredLine(r)).map(_.trim).filterNot(
-            r => r == "" || r == "\n")
+          r => nonDeterministicLine(r) || ignoredLine(r)).map(_.trim).filterNot(_ == "")
       case plan => if (isSorted(plan)) answer else answer.sorted
     }
     orderedAnswer.map(cleanPaths)

sql/hive/src/test/scala/org/apache/spark/sql/hive/execution/HiveCompatibilitySuite.scala

@@ -78,7 +78,7 @@ class HiveCompatibilitySuite extends HiveQueryFileTest with BeforeAndAfter {
     "alter_merge",
     "alter_concatenate_indexed_table",
     "protectmode2",
-    "describe_table",
+    //"describe_table",
     "describe_comment_nonascii",
     "udf5",
     "udf_java_method",
@@ -185,7 +185,7 @@ class HiveCompatibilitySuite extends HiveQueryFileTest with BeforeAndAfter {
     "describe_formatted_view_partitioned_json",
 
     // Hive returns the results of describe as plain text. Comments with multiple lines
-    // introduce extra in the Hive results, which make the result comparison fail.
+    // introduce extra lines in the Hive results, which make the result comparison fail.
     "describe_comment_indent"
   )