MySQL 5.6 - 类似 DENSE_RANK 的功能，没有 Order By

Question

我有一个这样的表:

+------+-----------+
|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，这样相同的 groupVarian 值具有由 nameVarian 表示的相同排名(例如:v1， v2 等等)。但是，分配给特定 groupVarian 的 nameVarian 值应该按照 caseID 的顺序(按照它们在表中出现的顺序)。

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's version is 5.6 ):

问题陈述看起来需要 DENSE_RANK groupVarian 的功能；然而事实并非如此。 As explained by @Gordon Linoff :

You appear to want them enumerated by the order they appear in the data.

假设您的表名称是 t(请根据您的代码相应地更改表和字段名称)。这是一个 approach utilizing session variables (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。尽管也可以稍微调整之前的查询以实现 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，并且避免了groupVarian 上的JOIN:

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