MySQL 查询获取书籍的阅读唯一页面数

Question

用户提交他/她在特定内容中阅读的起始页和结束页的间隔 书。请注意，用户可以为同一本书提交多个间隔。 我需要查询宣布系统中最推荐的五本书，这些书是根据已阅读的唯一页面数来挑选的 在第一次操作中提交间隔的所有用户（按阅读页数最多的书籍到阅读页数最少的书籍排序）。

book_user 表是我需要查询的数据透视表，因此如何获取插入记录的以下结果：

阅读间隔：

User 1 read from page 10 to page 30 in Book 1
User 2 read from page 2 to page 25 in Book 1
User 1 read from page 40 to page 50 in Book 2
User 3 read from page 1 to page 10 in Book 2
The most read books results:
Book 1 -> 28 pages
Book 2 -> 20 pages

我尝试这个查询：

select 'book_id',books.name as book_name,SUM(end_page - start_page) AS num_of_read_pages FROM book_user JOIN books ON books.id=book_user.book_id GROUP BY book_id ORDER BY num_of_read_pages DESC;

但是它没有获得重叠间隔的唯一页面

当我问chatgpt时，它给了我这个递归cte查询，但它不起作用，只是循环

WITH RECURSIVE cte AS (
    SELECT book_id, MIN(start_page) AS start_page, MAX(end_page) AS end_page
    FROM book_user
    GROUP BY book_id, start_page
    UNION ALL
    SELECT cte.book_id, cte.start_page, cte.end_page
    FROM cte
    JOIN book_user ON cte.book_id = book_user.book_id AND cte.start_page <= book_user.start_page AND cte.end_page >= book_user.end_page
)
SELECT book_id, SUM(end_page - start_page + 1) AS total_pages
FROM cte
GROUP BY book_id
ORDER BY total_pages DESC;

Answer 1

参见示例

with recursive  t as( 
     -- join ranges with same start_page 
     -- and row_number() for sequence join
  select book_id,start_page,max(end_page)end_page
    ,row_number()over(partition by book_id order by start_page) rn
  from book_user
  group by book_id,start_page
)
,r as(  -- recursive join 
     -- anchor - ranges with a "free" start_page
  select 0 lvl,bu.book_id,bu.start_page,bu.end_page,bu.rn
  from t bu
  where not exists(select 1 from t bu2 
         where bu2.book_id=bu.book_id and bu2.rn<bu.rn
           and bu.start_page between bu2.start_page and bu2.end_page)
  union all
  select lvl+1,r.book_id,r.start_page,t.end_page,t.rn
  from r inner join t on t.book_id=r.book_id and t.rn>r.rn
       and r.end_page between t.start_page and r.end_page
)
select book_id,sum(end_page-start_page+1) total_pages
from ( -- again, we group segments with the same start_page and different end_page
      select book_id,start_page,max(end_page) end_page 
      from r 
      group by book_id,start_page
  ) gr
group by book_id

详细信息在这里演示

输出

书号	总页数	路径
1	38	2-2:25,26,2:25,26:31,33-33:40
2	25	1-1:10,1:10:11,1:10:11:14,40-40:50
3	31	1-1:10,20-20:40

测试数据

create table books(id int,book_name varchar(20));
insert into books values(1,'Book 1'),(2,'Book 2'),(3,'Book 3');
create table users(id int,user_name varchar(20));
insert into users values(10,'User 10'),(20,'User 20'),(30,'User 40'),(30,'User 40');
create table book_user(user_id int,book_id int,start_page int,end_page int);
insert into book_user values
 (10,1, 10,30)
,(20,1,  2,25)
,(30,1,  2,26)
,(30,1, 10,31)
,(40,1, 33,40)
,(10,2, 40,50)
,(30,2,  1,10)
,(40,2, 10,11)
,(20,2, 11,14)
,(10,3,  1,10)
,(20,3, 20,40)
;