3

我有一个名为 users 的简单表，其中包含以下数据：

id | hops
 1 | 3
 2 | 1
 3 | 5
 4 | 2
 5 | 6
 6 | 5

我想根据降序排序的跳数进行上一个/下一个导航。我使用以下查询进行降序排序：

SELECT * FROM users ORDER BY hops DESC, id DESC

这是结果：

id | hops
 5 | 6
 6 | 5
 3 | 5
 1 | 3
 4 | 2
 2 | 1

现在我想要的是，当我在 mysql 查询中输入任何 id 时，我会根据上面的排序获得上一个和下一个 id。例如：

对于 id 5（在这种情况下 id=5 具有最高的跃点，因此之前没有以前的记录）：

id (current) | hops (current) | id (prev) | hops (prev) | id (next) | hops (next)
   5         |    6           |  NULL     | NULL        |  6        |  5

对于 id 6：

id (current) | hops (current) | id (prev) | hops (prev) | id (next) | hops (next)
   6         |    5           |  5        |     6       |  3        |  5

对于 ID 3：

id (current) | hops (current) | id (prev) | hops (prev) | id (next) | hops (next)
   3         |    5           |  6        |    5        |  1        |  3

对于 ID 1：

id (current) | hops (current) | id (prev) | hops (prev) | id (next) | hops (next)
   1         |    3           |  3        |    5        |  4        |  2

对于 id 4：

id (current) | hops (current) | id (prev) | hops (prev) | id (next) | hops (next)
   4         |    2           |  1        | 3           |  2        |  1

对于 id 2 （在这种情况下 id=2 具有最低的跃点，因此在它之后没有下一条记录）

id (current) | hops (current) | id (prev) | hops (prev) | id (next) | hops (next)
   2         |    1           |  4        | 2           |  NULL     |  NULL

谢谢

4

2 回答 2

2

尝试：

select cp.*, n.id id_next, n.hops hops_next
from
(select c.id id_current, c.hops hops_current, p.id id_previous, p.hops hops_previous
 from
 (select * from users where id = ?) c
 left join users p on c.hops < p.hops or (c.id < p.id and c.hops = p.hops)
 order by p.hops, p.id limit 1) cp 
left join users n 
       on cp.hops_current > n.hops or (cp.id_current > n.id and cp.hops_current = n.hops)
order by n.hops desc, n.id desc limit 1

（这里的 SQLFiddle ）

于 2013-04-04T11:11:23.207 回答
2

这是迄今为止我见过的最奇怪的用户表。无论如何，这是一种方法（尽管我不得不承认它有点复杂）......

DROP TABLE IF EXISTS test;

CREATE TABLE test(id INT NOT NULL AUTO_INCREMENT PRIMARY KEY,hops INT NOT NULL);

INSERT INTO test VALUES
(1 ,3),(2 ,1),(3,5),(4 ,2),(5 ,6),(6 ,5);

SELECT c.id id_curr
     , c.hops hops_curr
     , p.id id_prev
     , p.hops hops_prev
     , n.id id_next
     , n.hops hops_next
  FROM
     (
       SELECT a.*
            , COUNT(*) new_rank
         FROM 
            ( SELECT x.*
                   , COUNT(*) rank 
                FROM test x 
                JOIN test y 
                  ON y.hops >= x.hops 
               GROUP 
                  BY x.id
            ) a
         JOIN 
            ( SELECT x.*
                   , COUNT(*) rank 
                FROM test x 
                JOIN test y 
                  ON y.hops >= x.hops 
               GROUP 
                  BY x.id
            ) b
           ON b.rank < a.rank
           OR (b.rank = a.rank AND b.id >= a.id)
        GROUP 
           BY a.id
     )c
  LEFT
  JOIN
     (
       SELECT a.*
            , COUNT(*) new_rank
         FROM 
            ( SELECT x.*
                   , COUNT(*) rank 
                FROM test x 
                JOIN test y 
                  ON y.hops >= x.hops 
               GROUP 
                  BY x.id
            ) a
         JOIN 
            ( SELECT x.*
                   , COUNT(*) rank 
                FROM test x 
                JOIN test y 
                  ON y.hops >= x.hops 
               GROUP 
                  BY x.id
            ) b
           ON b.rank < a.rank
           OR (b.rank = a.rank AND b.id >= a.id)
        GROUP 
           BY a.id
     ) p
    ON p.new_rank = c.new_rank-1
  LEFT
  JOIN
     (
       SELECT a.*
            , COUNT(*) new_rank
         FROM 
            ( SELECT x.*
                   , COUNT(*) rank 
                FROM test x 
                JOIN test y 
                  ON y.hops >= x.hops 
               GROUP 
                  BY x.id
            ) a
         JOIN 
            ( SELECT x.*
                   , COUNT(*) rank 
                FROM test x 
                JOIN test y 
                  ON y.hops >= x.hops 
               GROUP 
                  BY x.id
            ) b
           ON b.rank < a.rank
           OR (b.rank = a.rank AND b.id >= a.id)
        GROUP 
           BY a.id
     ) n
    ON n.new_rank = c.new_rank+1
 ORDER 
    BY c.hops DESC
     , c.id DESC;
于 2013-04-04T11:19:06.080 回答