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> cume_dist 窗口函数的文档

# cume_dist

计算某个值在一组值中的累积分布，即值小于或等于当前行值的行所占的百分比。可用于确定某个值在分区中的相对位置。

**语法**

```sql theme={null}
cume_dist ()
  OVER ([[PARTITION BY grouping_column] [ORDER BY sorting_column]
        [RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING]] | [window_name])
FROM table_name
WINDOW window_name as ([PARTITION BY grouping_column] [ORDER BY sorting_column] RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING)
```

默认且必需的窗口帧定义为 `RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING`。

有关窗口函数语法的更多信息，请参见：[Window Functions - Syntax](/zh/reference/functions/window-functions#syntax)。

**返回值**

* 当前行的相对排名。返回类型为 Float64，取值范围是 \[0, 1]。[Float64](/zh/reference/data-types/float)。

**示例**

以下示例计算团队内薪资的累积分布：

```sql title="Query" theme={null}
CREATE TABLE salaries
(
    `team` String,
    `player` String,
    `salary` UInt32,
    `position` String
)
Engine = Memory;

INSERT INTO salaries FORMAT Values
    ('Port Elizabeth Barbarians', 'Gary Chen', 195000, 'F'),
    ('New Coreystad Archdukes', 'Charles Juarez', 190000, 'F'),
    ('Port Elizabeth Barbarians', 'Michael Stanley', 150000, 'D'),
    ('New Coreystad Archdukes', 'Scott Harrison', 150000, 'D'),
    ('Port Elizabeth Barbarians', 'Robert George', 195000, 'M'),
    ('South Hampton Seagulls', 'Douglas Benson', 150000, 'M'),
    ('South Hampton Seagulls', 'James Henderson', 140000, 'M');
```

```sql title="Query" theme={null}
SELECT player, salary,
       cume_dist() OVER (ORDER BY salary DESC) AS cume_dist
FROM salaries;
```

```response title="Response" theme={null}
   ┌─player──────────┬─salary─┬───────────cume_dist─┐
1. │ Robert George   │ 195000 │  0.2857142857142857 │
2. │ Gary Chen       │ 195000 │  0.2857142857142857 │
3. │ Charles Juarez  │ 190000 │ 0.42857142857142855 │
4. │ Douglas Benson  │ 150000 │  0.8571428571428571 │
5. │ Michael Stanley │ 150000 │  0.8571428571428571 │
6. │ Scott Harrison  │ 150000 │  0.8571428571428571 │
7. │ James Henderson │ 140000 │                   1 │
   └─────────────────┴────────┴─────────────────────┘
```

**实现细节**

`cume_dist()` 函数按以下公式计算相对位置：

```text theme={null}
cume_dist = (number of rows ≤ current row value) / (total number of rows in partition)
```

值相等的行 (并列行) 会获得相同的累积分布值，该值对应于该并列组中的最高位置。