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有人能简化我们使用关联嵌套子查询的方式和原因吗?我理解嵌套查询,但似乎无法理解相关嵌套查询的逻辑。
下面是一个例子。我有两张桌子供电影租赁数据库使用。
表租赁有关于租用电影的信息。表 customers 拥有关于租用它的客户的信息。
下面是嵌套查询的内容:
SELECT *
FROM CUSTOMERS
WHERE CUSTOMER_ID IN
-- nested to find customers with less than 5 rentals
(SELECT CUSTOMER_ID
FROM RENTING
GROUP BY CUSTOMER_ID
HAV