[SPARK-6744][SQL] Add support for CROSS JOIN syntax.

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/SqlParser.scala

@@ -61,6 +61,7 @@ class SqlParser extends AbstractSparkSQLParser with DataTypeParser {
   protected val CAST = Keyword("CAST")
   protected val COALESCE = Keyword("COALESCE")
   protected val COUNT = Keyword("COUNT")
+  protected val CROSS = Keyword("CROSS")
   protected val DESC = Keyword("DESC")
   protected val DISTINCT = Keyword("DISTINCT")
   protected val ELSE = Keyword("ELSE")
@@ -164,7 +165,7 @@ class SqlParser extends AbstractSparkSQLParser with DataTypeParser {
   // Based very loosely on the MySQL Grammar.
   // http://dev.mysql.com/doc/refman/5.0/en/join.html
   protected lazy val relations: Parser[LogicalPlan] =
-    ( relation ~ rep1("," ~> relation) ^^ {
+    ( relation ~ rep1(("," | CROSS ~ JOIN) ~> relation) ^^ {
         case r1 ~ joins => joins.foldLeft(r1) { case(lhs, r) => Join(lhs, r, Inner, None) } }
     | relation
     )

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/SqlParserSuite.scala

@@ -58,4 +58,11 @@ class SqlParserSuite extends FunSuite {
     assert(TestCommand("NotRealCommand") === parser("execute NotRealCommand"))
     assert(TestCommand("NotRealCommand") === parser("exEcute NotRealCommand"))
   }
+
+  test("cross join") {
+    val parser = new SqlParser
+    assert(parser("SELECT * FROM t1, t2") === parser("SELECT * FROM t1 CROSS JOIN t2"))
+    intercept[RuntimeException](parser("SELECT * FROM t1 CROSS JOIN t2 ON t1.a = t2.a"))
+  }
+
 }