MySQL 5.7 Reference Manual Including MySQL NDB Cluster 7.5 and NDB Cluster 7.6
        If a stored procedure exits with an unhandled exception,
        modified values of OUT and
        INOUT parameters are not propogated back to
        the caller.
      
        If an exception is handled by a CONTINUE or
        EXIT handler that contains a
        RESIGNAL statement, execution of
        RESIGNAL pops the Diagnostics
        Area stack, thus signalling the exception (that is, the
        information that existed before entry into the handler). If the
        exception is an error, the values of OUT and
        INOUT parameters are not propogated back to
        the caller.