每3条记录分组

Question

如何实现这一点（SQL）？

我的表

id    sub
1      1
2      1
3      1
4      1
5      1
6      2
7      2
8      2

结果应如下所示

groupid   id   sub              groupid    id    sub
   0       1    1                   0       1    1
   0       2    1                   0       2    1
   0       3    1                   0       3    1
   1       4    1         or        1       6    2
   1       5    1                   1       7    2
   2       6    2                   1       8    2
   2       7    2
   2       8    2

我目前的查询是

SELECT (id - 1) / 3 groupid, id, point FROM student

Answer 1

编辑：我原来答案中的第一个DENSE_RANK()可以被删除，以便最终得到;

WITH cte AS (
  SELECT ROW_NUMBER() OVER (PARTITION BY SUB ORDER BY ID) as rn, id, sub
FROM student)
SELECT DENSE_RANK() OVER (ORDER BY sub,(rn-1)/3) as groupid, id, sub FROM cte;

An SQLfiddle to test with。

- 原始答案 -

假设SQL服务器，您可以使用DENSE_RANK();

WITH cte AS (
  SELECT DENSE_RANK() OVER (ORDER BY sub) AS rank,
         ROW_NUMBER() OVER (PARTITION BY SUB ORDER BY ID) as rn,
       id, sub
FROM student)
SELECT DENSE_RANK() OVER (ORDER BY sub,rank,(rn-1)/3) as groupid,
id,sub FROM cte;

An SQLfiddle to test with

Answer 2

SELECT (id - 1) div 3 as groupid, id, point FROM student