164. View the Exhibit and examine the structure of CUSTOMERS and SALES tables.
Evaluate the following SQL statement:
UPDATE (SELECT prod_id, cust_id, quantity_sold, time_id
FROM sales)
SET time_id = '22-MAR-2007'
WHERE cust_id = (SELECT cust_id
FROM customers
WHERE cust_last_name = 'Roberts' AND
credit_limit = 600);
Which statement is true regarding the execution of the above UPDATE statement?
A. It would not execute because two tables cannot be used in a single UPDATE statement.
B. It would not execute because the SELECT statement cannot be used in place of the table name.
C. It would execute and restrict modifications to only the columns specified in the SELECT statement.
D. It would not execute because a subquery cannot be used in the WHERE clause of an UPDATE
statement.
Answer: C
答案解析：
参考：http://blog.csdn.net/rlhua/article/details/12885143
UPDATE后面的SELECT语句相当于一个简单视图，执行并限制只能修改SELECT语句指定的列，前提确保子查询的的结果为一个值。