MySQL：在查询中使用之前对值列表进行排序

Question

我可以在查询中使用值列表之前对其进行排序吗？

点赞SELECT SORTINGFN(2,3,1) 并获得1,2,3？ SELECT 2,3,1 ORDER BY ??? ASC 之类的东西，但按什么排序？

我需要确保参数的顺序始终相同，以便从 MD5('1,2,3') 和 MD5('2,3,1') 获得相同的哈希

Answer 1

无表（为argx设置值）：

SELECT arg1,arg2,arg3,
   MD5(SELECT GROUP_CONCAT(col ORDER BY col) 
       FROM (SELECT arg1 AS col
             UNION ALL SELECT arg2 
             UNION ALL SELECT arg3) AS sub) AS md5_checksum

SqlFiddleDemo

输出：

╔════╦════╦════╦══════════════════════════════════╗
║ 1  ║ 2  ║ 3  ║           md5_checksum           ║
╠════╬════╬════╬══════════════════════════════════╣
║ 1  ║ 2  ║ 3  ║ 55b84a9d317184fe61224bfb4a060fb0 ║
║ 3  ║ 2  ║ 1  ║ 55b84a9d317184fe61224bfb4a060fb0 ║
║ 3  ║ 1  ║ 2  ║ 55b84a9d317184fe61224bfb4a060fb0 ║
╚════╩════╩════╩══════════════════════════════════╝

反正MD5是弱哈希算法。

---

SQL 可以做很多事情。问题是这种操作的好地方，什么时候可以在应用层做。

任意列表：

SELECT MD5(GROUP_CONCAT(val ORDER BY val)) AS md5_sum
FROM (
  SELECT SUBSTRING_INDEX(SUBSTRING_INDEX(t.results, ',', n.n), ',', -1) AS val
  FROM (SELECT '3,2,1,10,212,3123,1' AS results) AS t 
  CROSS JOIN 
  (
     SELECT a.N + b.N * 10 + 1 n
       FROM 
      (SELECT 0 AS N UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) a
     ,(SELECT 0 AS N UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) b
  ) n
  WHERE n.n <= 1 + (LENGTH(t.results) - LENGTH(REPLACE(t.results, ',', '')))
) sub

SqlFiddleDemo2

输出：

╔══════════════════════╦══════════════════════════════════╗
║        args          ║             md5_sum              ║
╠══════════════════════╬══════════════════════════════════╣
║ 3,2,1,10,212,3123,1  ║ e2003296ed64cb59be61558275e22433 ║
║ 212,3123,1,3,2,1,10  ║ e2003296ed64cb59be61558275e22433 ║
╚══════════════════════╩══════════════════════════════════╝