MySQL查询计算特定日期范围内的用户保留

Question

我正在尝试选择保留在特定日期范围内的用户数，并且使用此查询和下表成功:

+----------+-------------+
| Field    | Type        |
+----------+-------------+
| id       | varchar(17) |
| log_date | date        |
+----------+-------------+

SELECT last_day.log_date, COUNT(distinct last_day.id) as users_num
FROM (SELECT DISTINCT log_date, id
      FROM `userActivity`) this_day
JOIN (SELECT DISTINCT log_date, id
      FROM `userActivity`) last_day
ON this_day.id = last_day.id
AND this_day.log_date = "2018-10-01"
AND last_day.log_date BETWEEN "2018-10-01" AND "2018-10-30"
GROUP BY log_date;

但我面临的问题是我想假设日期范围内的每一天都是第 0 天。(类似于以下示例):

请注意，图片中的第一行是我需要计算的以下结果的平均值。任何人都知道如何增强我的查询以获得如图所示的结果？

Answer 1

此解决方案仅适用于 MySQL 8.x，因为它需要 CTE(通用表表达式):

with digits as (
  select 0 as n union select 1 union select 2 union select 3 union select 4
  union select 5 union select 6 union select 7 union select 8 union select 9
),
series as (
select d1.n * 100 + d2.n * 10 + d3.n as n -- number series from 0 to 999
from digits d1
cross join digits d2
cross join digits d3
)
SELECT last_day.log_date, COUNT(distinct last_day.id) as users_num,
       date_add("2018-10-01", interval s.n day) as current_start
FROM (SELECT DISTINCT log_date, id
      FROM `userActivity`) this_day
JOIN (SELECT DISTINCT log_date, id
      FROM `userActivity`) last_day
ON this_day.id = last_day.id
cross join series s
WHERE s.n <= 30
  AND this_day.log_date = date_add("2018-10-01", interval s.n day)
  AND last_day.log_date BETWEEN date_add("2018-10-01", interval s.n day) 
                            AND date_add("2018-10-30", interval s.n day)
GROUP BY log_date, date_add("2018-10-01", interval s.n day);