CLEAR
ON ERROR
CD SYS(2023)
CREATE DATABASE trydatabase
CREATE TABLE trytable (ff1 I NULL DEFAULT RECNO(), ff2 i NULL DEFAULT NULL CHECK ff2#0)
WAIT WINDOWS "YOU CAN SEE THAT THE NULL COLUMN IS FLAGGED !" NOWAIT NOCLEAR
MODIFY STRUCTURE
USE
USE trytable NOUPDATE 
WAIT WINDOWS "YOU CAN SEE THAT THE NULL COLUMN IS BLANK !" NOWAIT NOCLEAR
MODIFY STRUCTURE
WAIT CLEAR
CLOSE DATABASE
DELETE DATABASE trydatabase DELETETABLES