Github user hvanhovell commented on a diff in the pull request:

    https://github.com/apache/spark/pull/14132#discussion_r70885711
  
    --- Diff: 
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala
 ---
    @@ -1774,6 +1775,34 @@ class Analyzer(
       }
     
       /**
    +   * Substitute Hints.
    +   */
    +  object SubstituteHint extends Rule[LogicalPlan] {
    +    def apply(plan: LogicalPlan): LogicalPlan = plan transform {
    --- End diff --
    
    The current grammar allows multiple query hints in a query. What will 
happen if we do that? For example:
    ```SQL
    SELECT /*+ MAPJOIN(tbl_a, tbl_a) */
           *
    FROM   tbl_a A
           JOIN tbl_b B
            ON B.id = A.id
           JOIN (SELECT /*+ MAPJOIN(tbl_c) */ 
                             XA.id
                      FROM   tbl_b XA
                              LEFT SEMI JOIN tbl_c XB
                              ON XB.id = XA.id) C
            ON C.id = A.id
    ```


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