create table ("vehicles.dbf") name "vehicles_t"(;
vehicle_id   i     not null,;
vehicle_code c( 8 )  not null,;
primary key vehicle_id tag "id")

Create SQL View vehicle_r AS ;
SELECT ;
VEHICLES_T.VEHICLE_ID,;
VEHICLES_T.VEHICLE_CODE,;
FROM  VEHICLES_T;
WHERE  VEHICLES_T.VEHICLE_ID = ?G_VEHICLE_ID

G_VEHICLE_ID = .null.
use vehicle_r 
или
select * from vehicles_t where vehicle_id = .null.

select * from vehicles_t where vehicle_id is null

select * from vehicles_t where vehicle_code = .null.