A.DROP CONSTRAINT EMP_FK_DEPT FROM雇員 B.DELETE CONSTRAINT EMP_FK_DEPT FROM雇員 C.ALTER TABLE雇員DROP CONSTRAINT EMP_FK_DEPT D.ALTER TABLE雇員REMOVE CONSTRAINT EMP_FK_DEPT
以下SQL命令執(zhí)行什么操作() ALTER TABLE employees ADD CONSTRAINT emp_manager_fk FOREIGN KEY(manager_id) REFERENCES employees(employee_id).
A.更改employees表并禁用emp_manager_fk約束條件 B.向EMPLOYEES表添加FOREIGN KEY約束條件,要求經(jīng)理必須已是雇員 C.向EMPLOYEES表添加FOREIGN KEY約束條件,要求經(jīng)理標(biāo)識(shí)應(yīng)匹配每個(gè)雇員標(biāo)識(shí) D.更改employees表并添加FOREIGN KEY約束,要求每個(gè)雇員標(biāo)識(shí)必須唯一
A.ALTER TABLE salary ADD CONSTRAINT fk_employee_id_01 FOREIGN KEY(employee_id)REFERENCES employees(employee_id) B.ALTER TABLE salary ADD CONSTRAINT fk_employee_id_ FOREIGN KEY BETWEEN salary(employee_id)AND employees(employee_id) C.ALTER TABLE salary FOREIGN KEY CONSTRAINT fk_employee_id_REFERENCES employees(employee_id) D.ALTER TABLE salary ADD CONSTRAINT fk_employee_id_FOREIGN KEY salary(employee_id)=employees(employee_id)