查看展品並檢查 ORDERS 表。ORDERS 名稱 空?類型 ORDER ID NOT NULL NUMBER(4) ORDATE DATE DATE CUSTOMER ID NUMBER(3) ORDER TOTAL NUMBER(7,2) ORDERS 表包含數據,所有訂單都分配了一個客戶 ID。哪條語句會爲 CUSTOMER_ID 列添加 NOT NULL 約束?
A. LTER TABLE ordersMODIFY CONSTRAINT orders_cust_id_nn NOT NULL(customer_id);
B. LTER TABLE ordersADD CONSTRAINT orders_cust_id_nn NOT NULL(customer_id);
C. LTER TABLE ordersMODIFY customer_id CONSTRAINT orders_cust_nn NOT NULL (customer_id);
D. LTER TABLE ordersADD customer_id NUMBER(6)CONSTRAINT orders_cust_id_nn NOT NULL;