如何选择日期列表之间的时间范围？

Question

有一个名为＆＃34;记录＆＃34;。

的表格

userid | date
------ | ------
1      | 2017-08-21  
1      | 2017-08-22  
2      | 2017-08-22  
1      | 2017-08-23  
3      | 2017-08-23 

现在我需要三个SQL来计算用户ID。

select count(DISTINCT userid) from record where date between 2017-08-21  and 2017-08-23;

结果：3

select count(DISTINCT userid) from record where date between 2017-08-22  and 2017-08-23;

结果：3

select count(DISTINCT userid) from record where date between 2017-08-23  and 2017-08-23;

结果：2

我想要算一次，有人可以帮我这个吗？

Answer 1

SELECT distinct date_field,
       (select count(distinct userid) from record r1 where r1.date_field between r2.date_field and '2017-08-23')
  FROM record r2

或者谢尔登提出的这个更高效的版本

SELECT date_field,
       (select count(distinct userid) from record r1 where r1.date_field between r2.date_field and '2017-08-23')
  FROM (select distinct date_field from record) r2

Answer 2

使用条件聚合：

select count(distinct case when between '2017-08-21' and '2017-08-23' then userid end),
       count(distinct case when between '2017-08-22' and '2017-08-23' then userid end),
       count(distinct case when between '2017-08-24' and '2017-08-23' then userid end)
from record r;