Select 一组随机一行（Oracle 10g）

Question

这个 post 与的相似之处在于我每组都有多个观察值。但是，我只想随机 select 其中一个 。我也在研究 Oracle 10g。

table df 中的每个 person_id 有多行。我想按 dbms_random.value() 和 select 每组的第一个观察值对每组 person_id 进行排序。为此，我尝试了：

select
    person_id, purchase_date
from
    df
where
    row_number() over (partition by person_id order by dbms_random.value()) = 1

查询returns:

ORA-30483: window functions are not allowed here 30483. 00000 - "window functions are not allowed here" *Cause: Window functions are allowed only in the SELECT list of a query. And, window function cannot be an argument to another window or group function.

Answer 1

使用子查询：

select person_id, purchase_date
from (select df.*,
             row_number() over (partition by person_id order by dbms_random.value()) as seqnum
      from df
     ) df
where seqnum = 1;

Answer 2

一个选项是使用 WITH..AS 子句：

WITH t AS
(
 SELECT df.*,
        ROW_NUMBER() OVER (PARTITION BY person_id ORDER BY dbms_random.value()) AS rn    
   FROM df
)    
SELECT person_id, purchase_date
  FROM t
 WHERE rn = 1

Answer 3

聚合查询（使用 GROUP BY 和聚合函数）比执行相同工作的等效分析函数快得多。因此，如果您有大量数据要处理，或者如果数据不是特别大但您必须运行经常执行此查询，您可能需要使用聚合而不是分析函数的更高效查询。

这是一种可能的方法：

select person_id, 
       max(purchase_date) keep (dense_rank first order by dbms_random.value()) 
           as random_purchase_date
from   df
group  by person_id
;

Select 一组随机一行（Oracle 10g）

Select one random row by group (Oracle 10g)

sql

oracle

random

group-by

oracle10g