Question

我要选择以下细分。

Random 5500 rows including the following segments:
       Subcategorie (sex): - 3300 men
                           - 2200 women
              Subcategorie (age): - 2140 between 18-34 years
                                  - 2100 between 35-54 years
                                  - 1260 between 55-99 years

如何在选择语句中解决此问题？

Answer 1

问题是，您使用“随机”一词，但是按年龄和性别划分的同类群组非常准确。真正随机的单个查询不会产生如此精确的配额。因此，您的查询必然很复杂：您需要将整个表划分为满足约束条件的子集，然后从这些子集中随机选择。像这样...

select * from (
   select * from whatever
   where sex = 'M'
   and age between 18 and 34
   order by dbms_random.value 
)
where rownum <= 1284
union all
select * from (
   select * from whatever
   where sex = 'M'
   and age between 35 and 54
   order by dbms_random.value 
)
where rownum <= 1260
union all    select * from (
   select * from whatever
   where sex = 'M'
   and age between 55 and 99
   order by dbms_random.value 
)
where rownum <= 756
union all
select * from (
   select * from whatever
   where sex = 'F'
   and age between 18 and 34
   order by dbms_random.value 
)
where rownum <= 856
union all
select * from (
   select * from whatever
   where sex = 'F'
   and age between 35 and 54
   order by dbms_random.value 
)
where rownum <= 840
union all    select * from (
   select * from whatever
   where sex = 'F'
   and age between 55 and 99
   order by dbms_random.value 
)
where rownum <= 504

这可能效果不佳，具体取决于通常的因素-表的大小，索引编制等-但它会产生那些确切的同类。

如果情况不太明显，则rownum界限是每个年龄段的点击次数乘以男女之比（3：2）。

Oracle随机段选择

1 个答案: