I agree that Help is confusing here. However the foxpro index file is not part of the SQL-92 standard, I believe. You will not get any errors if you remove primary key clause keeping "NOT NULL" for indexed field.
The error invokes because of the index file and "NOT NULL" for indexed field.


>Yuri, thanks for the response.
>
>It is still not clear for me:
>
>1) select * from vehicles_t where vehicle_code = .null.
>can be executed with no errors
>
>2) VFP help says - "Visual FoxPro support for null values complies with ANSI standards".
>The SQL-92 standard requires that an equals (=) or not equal to (<>) comparison against a null value evaluates to FALSE.
>
>From my point it means
>select * from vehicles_t where vehicle_id = .null.
>shouldn't raise any error and empty recordset should be returned
>
>Thank you