CLUSTER_SAMPLE

使用限制

窗口函数的使用限制如下：

• 窗口函数只能出现在select语句中。

• 窗口函数中不能嵌套使用窗口函数和聚合函数。

• 窗口函数不能和同级别的聚合函数一起使用。

命令格式

boolean cluster_sample(bigint <N>) OVER ([partition_clause])
boolean cluster_sample(bigint <N>, bigint <M>) OVER ([partition_clause])

命令说明

• cluster_sample(bigint <N>)：表示随机抽取N条数据。

• cluster_sample(bigint <N>, bigint <M>)：表示按比例（M/N）随机抽取。即抽取partition_row_count×M / N条数据。partition_row_count指分区中的数据行数。

参数说明

• N：必填。BIGINT类型常量。N为NULL时，返回值为NULL。

• M：必填。BIGINT类型常量。M为NULL时，返回值为NULL。

• partition_clause：可选。详情请参见frame_clause。

返回值说明

返回BOOLEAN类型。

示例数据

create table if not exists emp
   (empno bigint,
    ename string,
    job string,
    mgr bigint,
    hiredate datetime,
    sal bigint,
    comm bigint,
    deptno bigint);
tunnel upload emp.txt emp;   --请根据您上传数据文件的实际path(路径以及名称)替换emp.txt

7369,SMITH,CLERK,7902,1980-12-17 00:00:00,800,,20
7499,ALLEN,SALESMAN,7698,1981-02-20 00:00:00,1600,300,30
7521,WARD,SALESMAN,7698,1981-02-22 00:00:00,1250,500,30
7566,JONES,MANAGER,7839,1981-04-02 00:00:00,2975,,20
7654,MARTIN,SALESMAN,7698,1981-09-28 00:00:00,1250,1400,30
7698,BLAKE,MANAGER,7839,1981-05-01 00:00:00,2850,,30
7782,CLARK,MANAGER,7839,1981-06-09 00:00:00,2450,,10
7788,SCOTT,ANALYST,7566,1987-04-19 00:00:00,3000,,20
7839,KING,PRESIDENT,,1981-11-17 00:00:00,5000,,10
7844,TURNER,SALESMAN,7698,1981-09-08 00:00:00,1500,0,30
7876,ADAMS,CLERK,7788,1987-05-23 00:00:00,1100,,20
7900,JAMES,CLERK,7698,1981-12-03 00:00:00,950,,30
7902,FORD,ANALYST,7566,1981-12-03 00:00:00,3000,,20
7934,MILLER,CLERK,7782,1982-01-23 00:00:00,1300,,10
7948,JACCKA,CLERK,7782,1981-04-12 00:00:00,5000,,10
7956,WELAN,CLERK,7649,1982-07-20 00:00:00,2450,,10
7956,TEBAGE,CLERK,7748,1982-12-30 00:00:00,1300,,10

示例

• 随机抽取5条数据，命令示例如下：

  select deptno, sal    
  		from (        
        select deptno, sal, cluster_sample(5) over () as flag
        from emp
        ) sub 
       where flag = true;

  返回结果如下：

  +------------+------------+
  | deptno     | sal        |
  +------------+------------+
  | 30         | 2850       |
  | 30         | 1500       |
  | 20         | 3000       |
  | 10         | 2450       |
  | 10         | 1300       |
  +------------+------------+

• 随机抽取约20%的值，命令示例如下：

  select deptno, sal
      from (
          select deptno, sal, cluster_sample(5, 1) over () as flag
          from emp
          ) sub
      where flag = true;

  返回结果如下：

  +------------+------------+
  | deptno     | sal        |
  +------------+------------+
  | 10         | 2450       |
  | 20         | 3000       |
  | 20         | 3000       |
  +------------+------------+

• 从每组中抽取约20%的值，命令示例如下：

  select deptno, sal
      from (
          select deptno, sal, cluster_sample(5, 1) over (partition by deptno) as flag
          from emp
          ) sub
      where flag = true;

  返回结果如下：

  +------------+------------+
  | deptno     | sal        |
  +------------+------------+
  | 10         | 1300       |
  | 20         | 2975       |
  | 30         | 950        |
  +------------+------------+

相关函数

CLUSTER_SAMPLE函数属于窗口函数，更多对指定开窗列的数据进行求和、数值排序的相关函数请参见窗口函数。