MySQL 5.6 - DENSE_RANK 类似功能，没有 Order By

Question

我有一张这样的表：

+------+-----------+
|caseID|groupVarian|
+------+-----------+
|1     |A,B,C,D,E  |
+------+-----------+
|2     |A,B,N,O,P  |
+------+-----------+
|3     |A,B,N,O,P  |
+------+-----------+
|4     |A,B,C,D,F  |
+------+-----------+
|5     |A,B,C,D,E  |
+------+-----------+

我想获得一个新列nameVarian，以便相同的groupVarian值具有相同的排名nameVarian（例如：v1、v2 等）。但是，nameVarian分配给特定对象的值groupVarian应按照 的顺序caseID（按照它们出现在表中的顺序）。

输出应该是这样的：

+------+-----------+----------+
|caseID|groupVarian|namevarian
+------+-----------+----------+
|1     |A,B,C,D,E  |v1        |
+------+-----------+----------+
|2     |A,B,N,O,P  |v2        |
+------+-----------+----------+
|3     |A,B,N,O,P  |v2        |
+------+-----------+----------+
|4     |A,B,C,D,F  |v3        |
+------+-----------+----------+
|5     |A,B,C,D,E  |v1        |
+------+-----------+----------+

Answer 1

对于MySQL 版本 < 8.0（OP 的版本是 5.6）：

问题陈述看起来需要DENSE_RANK功能groupVarian；然而事实并非如此。正如@Gordon Linoff所解释的：

您似乎希望按照它们在数据中出现的顺序枚举它们。

假设您的表名是t（请根据您的代码相应地更改表名和字段名）。这是一种利用会话变量的方法（对于旧版本的 MySQL），给出所需的结果（DB Fiddle）：

SET @row_number = 0;
SELECT t3.caseID, 
       t3.groupVarian, 
       CONCAT('v', t2.num) AS nameVarian
FROM
  (
   SELECT 
     (@row_number:=@row_number + 1) AS num, 
     t1.groupVarian 
   FROM 
     (
      SELECT DISTINCT groupVarian 
      FROM t 
      ORDER BY caseID ASC 
     ) AS t1 
  ) AS t2 
INNER JOIN t AS t3 
  ON t3.groupVarian = t2.groupVarian 
ORDER BY t3.caseID ASC 

另外：我之前尝试模拟DENSE_RANK功能，效果很好。虽然之前的查询也可以稍微调整以实现DENSE_RANK功能。但是，以下查询效率更高，因为它创建了较少的派生表，并避免了JOIN on groupVarian：

SET @row_number = 1;
SET @group_varian = '';

SELECT inner_nest.caseID, 
       inner_nest.groupVarian, 
       CONCAT('v', inner_nest.num) as nameVarian 
FROM (
        SELECT 
            caseID, 
            @row_number:=CASE
                           WHEN @group_varian = groupVarian THEN @row_number
                           ELSE @row_number + 1
                         END AS num, 
            @group_varian:=groupVarian as groupVarian 
        FROM
            t  
        ORDER BY groupVarian
     ) AS inner_nest 
ORDER BY inner_nest.caseID ASC