按品质标志分组有何特点和作用？

A. INSERT INTO employees VALUES ( NULL, ‘John’,‘Smith’);
B. INSERT INTO employees( first_name, last_name) VALUES(‘John’,‘Smith’);
C. INSERT INTO employees VALUES (‘1000’,‘John’,NULL);
D. INSERT INTO employees(first_name,last_name, employee_id) VALUES ( 1000, ‘John’,‘Smith’);
E. INSERT INTO employees (employee_id) VALUES (1000);
F. INSERT INTO employees (employee_id, first_name, last_name) VALUES ( 1000, ‘John’,‘’)

A. 计划
B. 目标
C. 实施
D. 总结