Update SqlParser.scala

Author: YanjieGao

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

@@ -140,7 +140,8 @@ class SqlParser extends StandardTokenParsers with PackratParsers {
   protected lazy val query: Parser[LogicalPlan] = (
     select * (
         UNION ~ ALL ^^^ { (q1: LogicalPlan, q2: LogicalPlan) => Union(q1, q2) } |
-        UNION ~ opt(DISTINCT) ^^^ { (q1: LogicalPlan, q2: LogicalPlan) => Distinct(Union(q1, q2)) }
+        UNION ~ opt(DISTINCT) ^^^ { (q1: LogicalPlan, q2: LogicalPlan) => Distinct(Union(q1, q2)) } |
+        SUBTRACT  ^^^ { (q1: LogicalPlan, q2: LogicalPlan) => Subtract(q1, q2) } 
       )
     | insert | cache
   )