List TOK_ALTERTABLE as not explanable command.

Author: viirya

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

@@ -30,7 +30,8 @@ import org.apache.spark.sql.types.StructType
 
 private[sql] class SparkQl(conf: ParserConf = SimpleParserConf()) extends CatalystQl(conf) {
   /** Check if a command should not be explained. */
-  protected def isNoExplainCommand(command: String): Boolean = "TOK_DESCTABLE" == command
+  protected def isNoExplainCommand(command: String): Boolean =
+    "TOK_DESCTABLE" == command || "TOK_ALTERTABLE" == command
 
   protected override def nodeToPlan(node: ASTNode): LogicalPlan = {
     node match {
@@ -55,7 +56,7 @@ private[sql] class SparkQl(conf: ParserConf = SimpleParserConf()) extends Cataly
           getClauses(Seq("TOK_CREATETABLE", "FORMATTED", "EXTENDED"), explainArgs)
         ExplainCommand(nodeToPlan(crtTbl), extended = extended.isDefined)
 
-      case Token("TOK_EXPLAIN", explainArgs) =>
+      case Token("TOK_EXPLAIN", explainArgs) if "TOK_QUERY" == explainArgs.head.text =>
         // Ignore FORMATTED if present.
         val Some(query) :: _ :: extended :: Nil =
           getClauses(Seq("TOK_QUERY", "FORMATTED", "EXTENDED"), explainArgs)

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

@@ -147,7 +147,8 @@ private[hive] class HiveQl(conf: ParserConf) extends SparkQl(conf) with Logging
   protected val noExplainCommands = Seq(
     "TOK_DESCTABLE",
     "TOK_SHOWTABLES",
-    "TOK_TRUNCATETABLE"     // truncate table" is a NativeCommand, does not need to explain.
+    "TOK_TRUNCATETABLE",     // truncate table" is a NativeCommand, does not need to explain.
+    "TOK_ALTERTABLE"
   ) ++ nativeCommands
 
   /**