Dynamic runtime modifying SQL in datawindow

//let say we have these codes in open window event

string ls_code, ls_SQL, ls_newSQL

ls_code = message.stringparm
dw_1.settransobject(sqlca)

//get existing SQL from dw_1
ls_SQL = dw_1.getsqlselect( )

//dynamicly modify SQL in datawindow by adding where statement...
if ls_code = '-' then
    ls_newSQL = ls_SQL + " where b.KOD_JENIS IS NULL order by b.KOD_PEKA"
else
    ls_newSQL = ls_SQL + " where b.KOD_JENIS = '"+ls_code+"' order by b.KOD_PEKA"
end if

//sets new SQL to dw_1
dw_1.setsqlselect(ls_newSQL)
dw_1.retrieve()

/* example that you have this SQL in dw_1

select b.KOD, b.KOD_JENIS,
       (select c.PIHAK from ppihak c where c.KOD_PIHAK = b.KOD_PIHAK) as pihak,
       b.KOD_PTJ, b.TKH_TTGN, b.TKH_TAMAT, b.TKH_UPDATE, b.ID_UPDATE
from pmain b

*/