You can put null as I showed above or any value you like, try:
SELECT custno, SPACE(3) as type, SPACE(10) as bill_stat, CAST(null as n(5,2)) as numbs from test123 WHERE resto='5103'
SELECT custno, SPACE(3) as type, SPACE(10) as bill_stat, CAST(123 as n(5,2)) as numbs from test123 WHERE...