Hello Maurya,
You need only one record from dbtable so if you use all primary keys of dbtable then you will get only one record.
in select query use internal table itab instead field symbol.
and check for itab not initial.
then read itab into field symbol.
SELECT * FROM dbtable into table itab
WHERE condtEQ p_vendor (all primary keys).
if itab is not initial.
read itab into <fs_test>,
Endif.
Regards,
Kalpesh