带有组的SQL随机样本

Question

我有一个大学毕业生数据库,想要提取大约1000条记录的随机数据样本.

我想确保样本代表人口,所以希望包括相同比例的课程,例如

我可以使用以下方法执行此操作:

select top 500 id from degree where coursecode = 1 order by newid()
union
select top 300 id from degree where coursecode = 2 order by newid()
union
select top 200 id from degree where coursecode = 3 order by newid()

但是我们有数百个课程代码,所以这将耗费时间,我希望能够将这些代码重用于不同的样本大小,并且不特别想要通过查询和硬编码样本大小.

任何帮助将不胜感激

Answer 1

你想要一个分层的样本.我建议通过按课程代码对数据进行排序并执行第n个样本来完成此操作.如果您的人口规模很大,这里有一种最有效的方法:

select d.*
from (select d.*,
             row_number() over (order by coursecode, newid) as seqnum,
             count(*) over () as cnt
      from degree d
     ) d
where seqnum % (cnt / 500) = 1;

编辑:

您还可以"动态"计算每个组的人口规模:

select d.*
from (select d.*,
             row_number() over (partition by coursecode order by newid) as seqnum,
             count(*) over () as cnt,
             count(*) over (partition by coursecode) as cc_cnt
      from degree d
     ) d
where seqnum < 500 * (cc_cnt * 1.0 / cnt)