1、题目描述
Write an SQL query that reports the books that have sold less than 10 copies in the last year, excluding books that have been available for less than 1 month from today. Assume today is 2019-06-23.
The query result format is in the following example:
Books table:
| book_id | name | available_from |
|---|---|---|
| 1 | “Kalila And Demna” | 2010-01-01 |
| 2 | “28 Letters” | 2012-05-12 |
| 3 | “The Hobbit” | 2019-06-10 |
| 4 | “13 Reasons Why” | 2019-06-01 |
| 5 | “The Hunger Games” | 2008-09-21 |
Orders table:
| order_id | book_id | quantity | dispatch_date |
|---|---|---|---|
| 1 | 1 | 2 | 2018-07-26 |
| 2 | 1 | 1 | 2018-11-05 |
| 3 | 3 | 8 | 2019-06-11 |
| 4 | 4 | 6 | 2019-06-05 |
| 5 | 4 | 5 | 2019-06-20 |
| 6 | 5 | 9 | 2009-02-02 |
| 7 | 5 | 8 | 2010-04-13 |
Result table:
| book_id | name |
|---|---|
| 1 | “Kalila And Demna” |
| 2 | “28 Letters” |
| 5 | “The Hunger Games” |
来源：力扣（LeetCode）
2、解题思路
1# 增加子表，分别计算在2018年卖的数量
select book_id,sum(quantity) as qu
from Orders
where year(dispatch_date)=2018
group by book_id
2# Books表与上表联查，条件是上表卖的数小于10，并且与今天’2019-06-23’相差小于30
where ifnull(qu,0)<=10 and datediff('2019-06-23',available_from)>30
3、提交记录
select b.book_id,b.name
from Books b left join
(select book_id,sum(quantity) as qu
from Orders
where year(dispatch_date)=2018
group by book_id)jude
on b.book_id=jude.book_id
where ifnull(qu,0)<=10 and datediff('2019-06-23',available_from)>30
系统出错，无法通过
