是否可以通过查询获取组内组内的随机值？

Question

我想在分组查询中获得随机值，像这样：

SELECT city , SOME_RANDOMIZER_FUNC(latitude) as "RANDOM_LATITUDE_IN_CITY" , SOME_RANDOMIZER_FUNC(longitude) AS "RANDOM_LONGITUDE_IN_CITY" FROM some_table GROUP BY city

输入：

city LATITUDE LONGITUDE STO -31.3935 -57.9413 STO -31.0274 -57.8081 STO -30.7852 -57.7765 STO -30.4274 -56.4718 NDU -30.2747 -57.6023 NDU -32.2909 -58.0737 NDU -32.0286 -57.8468 NDU -32.3600 -57.2021 NDU -32.6816 -57.6541 MBO -31.7085 -55.9873 MBO -30.9359 -55.5457 MBO -31.1972 -55.7574 MBO -31.7711 -54.6904

期望的输出：

city RANDOM_LATITUDE_IN_CITY RANDOM_LONGITUDE_IN_CITY STO -31.0274 -57.9413 NDU -32.3600 -57.6541 MBO -30.9359 -55.5457

其中函数SOME_RANDOMIZER_FUNC returns一个组内的随机值.

Answer 1

在随机函数的输入参数中，您呈现所有数据，然后对其应用分组，这是不允许的。执行此操作的最佳方法是使用以下代码：

with s_table as (

    select
        city,
        latitude,
        longitude,
        row_number() over(partition by city order by DBMS_RANDOM.VALUE) as random_sort
    from
        some_table
    )
    select
    city,
    latitude,
    longitude
from
    s_table
where
    random_sort =1

Answer 2

为每个城市的行随机编号，然后保留编号为 1 的行。

SELECT city, latitude, longitude
FROM
(
  SELECT 
    city, latitude, longitude,
    ROW_NUMBER() OVER (PARTITION BY city ORDER BY DBMS_RANDOM.VALUE) AS rn
  FROM some_table
)
WHERE rn = 1
ORDER BY city;

Answer 3

如果你想要一些不确定的行，那么你可以尝试 any_value 函数，自 21c 起记录：

create table t
as
select
  trunc((level - 1)/10) as city
  , level as lat
  , 100 - level as lon
from dual
connect by level < 101

select /*+gather_plan_statistics*/
  city
  , any_value(lat) as lat
  , any_value(lon) as lon
from t
group by
  city

CITY | LAT | LON
---: | --: | --:
   0 |   1 |  99
   1 |  11 |  89
   2 |  21 |  79
   3 |  31 |  69
   4 |  41 |  59
   5 |  51 |  49
   6 |  61 |  39
   7 |  71 |  29
   8 |  81 |  19
   9 |  91 |   9

db<>fiddle here

Answer 4

您可以将 FIRST_VALUE 与 DBMS_RANDOM.VALUE

结合使用

例如：

SELECT city, latitude, longitude
FROM
(
    SELECT city
    , FIRST_VALUE(latitude) OVER (PARTITION BY city ORDER BY DBMS_RANDOM.VALUE) as latitude
    , FIRST_VALUE(longitude) OVER (PARTITION BY city ORDER BY DBMS_RANDOM.VALUE) as longitude
    FROM some_table
) 
GROUP BY city, latitude, longitude
ORDER BY city;

CITY | LATITUDE | LONGITUDE
:--- | -------: | --------:
MBO  | -30.9359 |  -55.5457
NDU  | -32.6816 |  -57.6541
STO  | -30.4274 |  -56.4718

演示 db<>fiddle here

是否可以通过查询获取组内组内的随机值？

Is it possible to get a random value within a group in a group by query?

sql

oracle

random

group-by

oracle11g