select rf.RDB$RELATION_NAME,
       rf.RDB$FIELD_NAME,
       vr.RDB$RELATION_NAME,
       rf.RDB$BASE_FIELD
  from RDB$RELATION_FIELDS rf
  join RDB$VIEW_RELATIONS  vr on ( vr.RDB$VIEW_NAME = rf.RDB$RELATION_NAME and
                                   vr.RDB$VIEW_CONTEXT = rf.RDB$VIEW_CONTEXT )
 where rf.RDB$RELATION_NAME = :RELATION_NAME;

select RDB$PROCEDURE_NAME,
       RDB$PARAMETER_NAME,
       RDB$RELATION_NAME,
       RDB$FIELD_NAME
  from RDB$PROCEDURE_PARAMETERS
 where RDB$PROCEDURE_NAME = :PROCEDURE_NAME
   and RDB$PARAMETER_TYPE = 1;

create procedure TEST
returns (
    SP_ID integer,
    SP_VAL varchar(10)
)
as
begin
  for
    select t1.ID, t2.VAL
      from TBL1 t1
      join TBL2 t2 on ( t2.REF_ID = t1.ID )
      into :SP_ID, :SP_VAL
  do
    suspend;
end

TEST.SP_ID  = TBL1.ID
TEST.SP_VAL = TBL2.VAL