How can I use UNION in mysql

code (Procedure):
<pre lang="SQL">
begin
DECLARE Mont INT default 1;
DECLARE StrDATE varchar(7) ;
DECLARE StrYearr varchar(7) ;
set StrYearr = StrYear ;
set StrDATE =  CONCAT(Mont,'-',StrYearr);

drop temporary table if exists TableHelp;
create temporary table TableHelp
(
    PeriodY year,
    PeriodM varchar(10),
    MtnSTaxes float,
    TypeEntr int
);
while (Mont <=12) do
    insert into TableHelp(PeriodY,PeriodM,MtnSTaxes,TypeEntr)
    (
     select (SecTabDatePaieY,SecTabDatePaieM,sum(SecTable.SumV_Prix),3)
     from (select Date_Format(p.DatePaie,"%Y")as SecTabDatePaieY,Date_Format(p.DatePaie,"%m-%Y")as SecTabDatePaieM,(select sum(V_Prix) from lsthelpget_montsansfrais where V_configYesNon=1 and V_IdPaie= p.IdPaie and V_IdFAct=p.IdFact) as SumV_Prix from paiement p where PayePaie=1) as SecTable
     where SecTable.SecTabDatePaieM=Date_Format(StrDATE,"%m-%Y") group by SecTable.SecTabDatePaieM asc UNION (select StrYearr,StrDATE,0,3)       
    );   
    set Mont= Mont+1 ;
END WHILE;
SELECT PeriodM,MtnSTaxes,TypeEntr from TableHelp;
end