histogram_numeric 聚合函数
适用于：
Databricks SQL Databricks Runtime 10.2 及更高版本
使用 numBins 箱计算 expr 上的直方图。
语法
histogram_numeric ( [ALL | DISTINCT ] expr, numBins ) [ FILTER ( WHERE cond ) ]
参数
expr：函数在其上使用和计算直方图的数字、TIMESTAMP、DATE或INTERVAL表达式。numBins：必须大于 1 的INTEGER文本，用于指定直方图计算的箱数。cond：可选的BOOLEAN表达式，用于筛选聚合的行。
返回
返回值为 ARRAY 或 STRUCTS，带有 x 和 y，表示直方图箱的中心。类型 x 与类型 expr 相同，类型 y 则为 DOUBLE。
增加 numBins 值会优化直方图近似值，从而使其更加精细。 但它可以在离群值周围引入伪影。
通常，20-40 个箱对于直方图是有效的，尽管倾斜或较小的数据集可能需要更多的箱。请注意，此函数会创建具有非统一箱宽度的直方图。
它在直方图的均方误差方面不提供任何保证，但实际上与其他计算包生成的直方图相当。
指定 DISTINCT 会导致函数仅对一组唯一的 expr 值进行操作。
示例
> SELECT histogram_numeric(col, 5)
FROM VALUES (0), (1), (2), (10) AS tab(col);
[{"x":0.0,"y":1.0},{"x":1.0,"y":1.0},{"x":2.0,"y":1.0},{"x":10.0,"y":1.0}]
> SELECT histogram_numeric(col, 5)
FROM VALUES (0L), (1L), (2L), (10L) AS tab(col);
[{"x":0,"y":1.0},{"x":1,"y":1.0},{"x":2,"y":1.0},{"x":10,"y":1.0}]
> SELECT histogram_numeric(col, 5)
FROM VALUES (0F), (1F), (2F), (10F) AS tab(col);
[{"x":0.0,"y":1.0},{"x":1.0,"y":1.0},{"x":2.0,"y":1.0},{"x":10.0,"y":1.0}]
> SELECT histogram_numeric(col, 5)
FROM VALUES (0D), (1D), (2D), (10D) AS tab(col);
[{"x":0.0,"y":1.0},{"x":1.0,"y":1.0},{"x":2.0,"y":1.0},{"x":10.0,"y":1.0}]
> SELECT histogram_numeric(col, 5)
FROM VALUES (INTERVAL 0 YEAR), (INTERVAL 1 YEAR), (INTERVAL 2 YEAR),
(INTERVAL 3 YEAR) AS tab(col);
[{"x":0-0,"y":1.0},{"x":1-0,"y":1.0},{"x":2-0,"y":1.0},{"x":3-0,"y":1.0}]
> SELECT histogram_numeric(col, 5)
FROM VALUES (INTERVAL 0 DAY), (INTERVAL 1 DAY), (INTERVAL 2 DAY),
(INTERVAL 3 DAY) AS tab(col);
[{"x":0 00:00:00.000000000,"y":1.0},{"x":1 00:00:00.000000000,"y":1.0},{"x":2 00:00:00.000000000,"y":1.0},{"x":3 00:00:00.000000000,"y":1.0}]
> SELECT histogram_numeric(col, 5)
FROM VALUES (TIMESTAMP '2020-01-01'), (TIMESTAMP'2020-02-01'),
(TIMESTAMP'2020-03-01'), (TIMESTAMP'2020-10-01') AS tab(col)
[{"x":2020-01-01 00:00:00,"y":1.0},{"x":2020-02-01 00:00:00,"y":1.0},{"x":2020-03-01 00:00:00,"y":1.0},{"x":2020-10-01 00:00:00,"y":1.0}]