79. View the Exhibit and examine the data in ORDERS_MASTER and
MONTHLY_ORDERS tables.
Evaluate the following MERGE statement:
MERGE INTO orders_master o USING monthly_orders m
ON (o.order_id = m.order_id)
WHEN MATCHED THEN UPDATE SET o.order_total = m.order_total
DELETE WHERE (m.order_total IS NULL)
A. The ORDERS_MASTER table would contain
the ORDER_IDs 1 and 2.
B. The ORDERS_MASTER table would contain
the ORDER_IDs 1, 2 and 3.
C. The ORDERS_MASTER table would contain
the ORDER_IDs 1, 2 and 4.
(right)
D. The ORDERS_MASTER table would contain
the ORDER_IDs 1, 2, 3 and 4.
当 o.order_id=m.order_i d 时，也就是 2 、 3 两条记录 UPDATE SET o.order_total
= m.order_total ，order_id=2记录的 order_total 改成了 2500,order_id=3记录的order_total改为order_total=null，符合 delete 条件，被删
除。目前剩下 1 、 2 、 4
WHEN NOT MATCHED THEN INSERT VALUES (m.order_id,
m.order_total);
分析如下：
疑问：
DELETE WHERE (m.order_total IS NULL) 但是没说o.order_total is null 删除 orders_master表中的第3行？
实验如下结果：
---------- -----------
1 1000
2 2500
4
good luck
来自 “ ITPUB博客 ” ，链接：https://blog.itpub.net/29674916/viewspace-1781644/ ，如需转载，请注明出处，否则将追究法律责任。
