Add left semi to SQL Parser.

Author: marmbrus

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

@@ -128,6 +128,7 @@ class SqlParser extends StandardTokenParsers with PackratParsers {
   protected val OUTER = Keyword("OUTER")
   protected val RIGHT = Keyword("RIGHT")
   protected val SELECT = Keyword("SELECT")
+  protected val SEMI = Keyword("SEMI")
   protected val STRING = Keyword("STRING")
   protected val SUM = Keyword("SUM")
   protected val TRUE = Keyword("TRUE")
@@ -238,6 +239,7 @@ class SqlParser extends StandardTokenParsers with PackratParsers {
 
    protected lazy val joinType: Parser[JoinType] =
      INNER ^^^ Inner |
+     LEFT ~ SEMI ^^^ LeftSemi |
      LEFT ~ opt(OUTER) ^^^ LeftOuter |
      RIGHT ~ opt(OUTER) ^^^ RightOuter |
      FULL ~ opt(OUTER) ^^^ FullOuter