本文探讨了如何使用SQL语句从PRODUCTS表中删除过去三年内没有销售记录的产品行。通过理解SALES表与PRODUCTS表之间的外键关系，并运用ON DELETE CASCADE选项，文章详细解释了正确构造DELETE语句的方法。
48、(10-12)choose the best answer
View the Exhibit and examine the description for the PRODUCTS and SALES table.
PROD_ID is a primary key in the PRODUCTS table and foreign key in the SALES table with ON DELETE CASCADE option. The SALES table contains data for the last three years. You want to remove all the rows from the PRODUCTS table for which no sale was done for the last three years.
Which is the valid DELETE statement?
A) DELETE
FROM products
WHERE prod id IN (SELECT prod_id
FROM sales
where time_id >= SYSDATE - 3*365 );
B) DELETE
FROM products
WHERE prod_id = (SELECT prod_id
FROM sales
WHERE time_id - 3*365 = SYSDATE );
C) DELETE
FROM products
WHERE prod_id = (SELECT prod_id
FROM sales
WHERE SYSDATE >= time_id - 3*365 );
D) DELETE
FROM products
WHERE prod_id IN (SELECT prod_id
FROM sales
where SYSDATE - 3*365 >= time_id);
Answer：A
(解析：time_id >= SYSDATE - 3*365 最近三年的时间
SYSDATE - 3*365 >= time_id 三年以前的时间
原来 051 的题
)
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