Question

我有一个MySQL表（简化）的以下模式，它有一个封装了层次结构的索引字段整个评论主题中的评论条目。

+----------+------------+-----+---------+----------------+
| id       | INTEGER    | PRI | NULL    | auto_increment |
| comment  | TEXT       |     | NULL    |                |
| index    | TEXT       |     | NULL    |                |
+----------+------------+-----+---------+----------------+

id: comment:                         index:
-------------------------------------------------------
1   Rootentry1                        1
2   Answer1 on Rootentry1             1.1
3   Rootentry2                        2
4   Answer1 on Answer1 on Rootentry1  1.1.1
5   Rootentry3                        3
6   Answer1 on Rootentry2             2.1
7   Answer2 on Rootentry1             1.2

现在我想以最先出现Rootentry的方式对表格进行排序。结果应按以下顺序排列：

id: comment:                         index:
------------------------------------------------------
5   Rootentry3                       3
3   Rootentry2                       2
6   Answer1 on Rootentry2            2.1
1   Rootentry1                       1
2   Answer1 on Rootentry1            1.1
4   Answer1 on Answer1 on Rootentry1 1.1.1
7   Answer2 on Rootentry1            1.2

我需要一种排序算法，以降序方式对第一个索引进行排序，并按升序方式对以下字符进行排序对这样的条目进行排序的声明是什么？

Answer 1

applicationDidBecomeActive

输出：

select 
*
from table1
order by 
cast(substring_index(`index`, '.', 1) as unsigned) desc,
substring(`index`, 2+length(substring_index(`index`, '.', 1))) asc

Answer 2

只是为了好玩......

DROP TABLE IF EXISTS my_table;

CREATE TABLE my_table(id INT NOT NULL AUTO_INCREMENT PRIMARY KEY,legal VARCHAR(12) NOT NULL UNIQUE);

INSERT INTO my_table (legal) VALUES ('1'),('1.1'),('2'),('1.1.1'),('3'),('2.1'),('1.2');

SELECT * FROM my_table;
+----+-------+
| id | legal |
+----+-------+
|  1 | 1     |
|  2 | 1.1   |
|  4 | 1.1.1 |
|  7 | 1.2   |
|  3 | 2     |
|  6 | 2.1   |
|  5 | 3     |
+----+-------+

SELECT *
     , FLOOR(INET_ATON(RPAD(legal,5,'.0'))/16000000) x -- or perhaps 16777216
  FROM my_table 
 ORDER 
    BY x DESC
     , legal;
+----+-------+------+
| id | legal | x    |
+----+-------+------+
|  5 | 3     |    3 |
|  3 | 2     |    2 |
|  6 | 2.1   |    2 |
|  1 | 1     |    1 |
|  2 | 1.1   |    1 |
|  4 | 1.1.1 |    1 |
|  7 | 1.2   |    1 |
+----+-------+------+

混合order by语句需要MySQL查询

2 个答案: