LINEAR_HISTOGRAM

描述

LINEAR_HISTOGRAM 函数用于描述数据分布情况，它使用“等宽”的分桶策略，并按照数据的值大小进行分桶。

语法

`LINEAR_HISTOGRAM(<expr>, DOUBLE <interval>[, DOUBLE <offset>)`

参数说明

参数	说明
interval	桶的宽度，支持类型为 TinyInt，SmallInt，Int，BigtInt，LargeInt，Float，Double，Decimal。
offset	可选。默认为 0，范围是 [0, interval)，支持类型为Double。

返回值

返回计算后的 JSON 类型的值。

举例

-- setup
create table histogram_test(
  a int
) distributed by hash(a) buckets 1
properties ("replication_num"="1");
insert into histogram_test values
  (0), (1), (2), (3), (4), (5), (6), (7), (8), (9), (10), (11), (null);

select linear_histogram(a, 2) from histogram_test;

+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| linear_histogram(a, 2)                                                                                                                                                                                                                                                                                                                         |
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| {"num_buckets":6,"buckets":[{"lower":0.0,"upper":2.0,"count":2,"acc_count":2},{"lower":2.0,"upper":4.0,"count":2,"acc_count":4},{"lower":4.0,"upper":6.0,"count":2,"acc_count":6},{"lower":6.0,"upper":8.0,"count":2,"acc_count":8},{"lower":8.0,"upper":10.0,"count":2,"acc_count":10},{"lower":10.0,"upper":12.0,"count":2,"acc_count":12}]} |
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

select linear_histogram(a, 2, 1) from histogram_test;

+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| linear_histogram(a, 2, 1)                                                                                                                                                                                                                                                                                                                                                                         |
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| {"num_buckets":7,"buckets":[{"lower":-1.0,"upper":1.0,"count":1,"acc_count":1},{"lower":1.0,"upper":3.0,"count":2,"acc_count":3},{"lower":3.0,"upper":5.0,"count":2,"acc_count":5},{"lower":5.0,"upper":7.0,"count":2,"acc_count":7},{"lower":7.0,"upper":9.0,"count":2,"acc_count":9},{"lower":9.0,"upper":11.0,"count":2,"acc_count":11},{"lower":11.0,"upper":13.0,"count":1,"acc_count":12}]} |
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

select linear_histogram(a, 2, 1) from histogram_test where a is null;

+--------------------------------+
| linear_histogram(a, 2, 1)      |
+--------------------------------+
| {"num_buckets":0,"buckets":[]} |

字段说明：

- `num_buckets`：桶的数量。
- `buckets`：直方图所包含的桶。
  - `lower`：桶的下界。（包含在内）
  - `upper`：桶的上界。（不包含在内）
  - `count`：桶内包含的元素数量。
  - `acc_count`：前面桶与当前桶元素的累计总量。