---
title: "APPROX_COUNT_DISTINCT - OceanBase Database AI V4.6.2 | OceanBase 文档中心"
description: APPROX_COUNT_DISTINCT 声明 APPROX_COUNT_DISTINCT(expr) OVER over_clause 说明 对表达式 expr 去重后的行数进行计算，结果只能返回一个值，且该值是近似值。处理大量数据时，速度明显快于 COUNT() ，与精确结果的偏差可以忽略不计。 示例 obcl…
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---
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文档反馈![](https://mdn.alipayobjects.com/huamei_22khvb/afts/img/A*inJjSpyNOjUAAAAAHtAAAAgAeiGDAQ/original) OceanBase Database AIV 4.6.2

# APPROX_COUNT_DISTINCT

更新时间：2026-08-13 19:27:48

[编辑](https://github.com/oceanbase/oceanbase-database-ai/edit/V4.6.2/zh-CN/700.reference/500.sql-reference/100.sql-syntax/200.common-tenant-of-mysql-mode/400.functions-of-mysql-mode/400.analysis-functions-of-mysql-mode/100.approx-count_distinct-of-mysql-mode.md)  

## 声明

```sql
APPROX_COUNT_DISTINCT(expr) OVER over_clause

```

## 说明

对表达式 `expr` 去重后的行数进行计算，结果只能返回一个值，且该值是近似值。处理大量数据时，速度明显快于 `COUNT()`，与精确结果的偏差可以忽略不计。

## 示例

```sql
obclient> CREATE TABLE employees (manager_id INT,last_name varchar(50),hiredate varchar(50),SALARY INT);
INSERT INTO employees VALUES(100, 'Raphaely', '2017-07-01', 1700);
INSERT INTO employees VALUES(100, 'De Haan', '2018-05-01',11000);
INSERT INTO employees VALUES(100, 'Errazuriz', '2017-07-21', 1400);
INSERT INTO employees VALUES(100, 'Hartstein', '2019-05-01',14000);
INSERT INTO employees VALUES(100, 'Raphaely', '2017-07-22', 1700);
INSERT INTO employees VALUES(100, 'Weiss',  '2019-07-11',13500);
INSERT INTO employees VALUES(100, 'Russell', '2019-10-05', 13000);
INSERT INTO employees VALUES(100, 'Partners',  '2018-12-01',14000);
INSERT INTO employees VALUES(200, 'Ross',  '2019-06-11',13500);
INSERT INTO employees VALUES(200, 'Bell', '2019-05-25', 13000);
INSERT INTO employees VALUES(200, 'Part',  '2018-08-11',14000);
COMMIT;

obclient> SELECT last_name, salary, APPROX_COUNT_DISTINCT(salary) OVER (ORDER BY hiredate) "Variance"
FROM employees WHERE manager_id = 100 ORDER BY last_name, salary, "Variance";
+-----------+--------+----------+
| LAST_NAME | SALARY | Variance |
+-----------+--------+----------+
| De Haan   |  11000 |        3 |
| Errazuriz |   1400 |        2 |
| Hartstein |  14000 |        4 |
| Partners  |  14000 |        4 |
| Raphaely  |   1700 |        1 |
| Raphaely  |   1700 |        2 |
| Russell   |  13000 |        6 |
| Weiss     |  13500 |        5 |
+-----------+--------+----------+

```

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