按固定数量的记录分区

Question

我想知道如何按固定数量的记录对窗口进行分区。

示例 (http://sqlfiddle.com/#!1/7df86)。

CREATE TABLE Games 
(
 id serial primary key, 
 game_no integer not null, 
 points integer,
  constraint game_no unique (game_no)
);

INSERT INTO Games (game_no, points)
VALUES (3123, 5), (3126, 5), (3135, 8), (3128, null), (3130, 1), (3121, 11), 
(3132, 0), (3133, 4), (3110, 7), (3112, null), (3113, 12), (3125, 3),(3134, 8);

我想要三场比赛的总和，从最高的比赛号码开始，按比赛号码降序排列。像这样。

| GAME_NO | POINTS | SUM_THREE |
|---------|--------|-----------|
|    3135 |      8 |        20 |
|    3134 |      8 |        20 |
|    3133 |      4 |        20 |
|    3132 |      0 |         1 |
|    3130 |      1 |         1 |
|    3128 | (null) |         1 |
|    3126 |      5 |        13 |
|    3125 |      3 |        13 |
|    3123 |      5 |        13 |
|    3121 |     11 |        23 |
|    3113 |     12 |        23 |
|    3112 | (null) |        23 |
|    3110 |      7 |         7 |

如何在不使用子查询的情况下使用窗口函数来实现这一点？我也不能使用例如 with 语句。它必须是一个查询，因为外部解析器将执行它（我无法控制）。看起来很简单，最近几天我都在琢磨它:)

Answer 1

您可以使用 row_number 函数除以 3 为每组 3 个连续行分配唯一编号。然后使用 sum 作为每个组的解析函数。

SQL Fiddle

with x(game_no, points, grp) as (
  select game_no, points,
         ceil(cast(row_number() over (order by game_no desc) as decimal)/ 3)
  from games
  )
select game_no, points,
       sum(points) over (partition by grp)
from x
order by game_no desc;

您可以使用内联视图代替 with 构造。

select game_no, points,
       sum(points) over (partition by grp)
from (
      select game_no, points,
             ceil(cast(row_number() over
                   (order by game_no desc) as decimal)/ 3) as grp
      from games
    ) as x
order by game_no desc;

Results：

| GAME_NO | POINTS | SUM |
|---------|--------|-----|
|    3135 |      8 |  20 |
|    3134 |      8 |  20 |
|    3133 |      4 |  20 |
|    3132 |      0 |   1 |
|    3130 |      1 |   1 |
|    3128 | (null) |   1 |
|    3126 |      5 |  13 |
|    3125 |      3 |  13 |
|    3123 |      5 |  13 |
|    3121 |     11 |  23 |
|    3113 |     12 |  23 |
|    3112 | (null) |  23 |
|    3110 |      7 |   7 |