PHP + Mysql - 获取过去 30 天中每一天的统计数据

Question

The table name is Users

ID | name  | created_at 
------------------------------------------
 1 | John  | 2018-11-08 14:06:05 
 2 | Adam  | 2018-12-12 10:06:05
 3 | Peter | 2019-01-08 17:16:05 
-------------------------------------------

How do I get how many new users i have received for each day of the last 30 days (using mysql or php or both). The results should look like this:

1-Sat  15
2-Sun  08
.
.
.
30-Fri 13

If the day has no records it shows 0.

I tried this but i get stuck:

select date_format(created_at,\'%a\') as day  
from users 
where datediff (now(),created_at) <=30

Thanks alot

Answer 1

Here is a solution in 3 steps :

1. generate a list of the last 30 days (see detailed solution here : Select last 30 days in MySQL

2. generate the number of registrations per day, with GROUP BY. It is a key concept in SQL database, so I invite you to learn it if you use SQL regularly : SQL Group By

3. Use a LEFT JOIN to keep all the dates in the calendar, and associate them to the number of registrations. If a day has no registration, the value will be NULL, so I used COALESCE to return 0 in this case

Full query :

SELECT calendar.day, COALESCE(daily_registrations.nb_created, 0)
FROM
( 
    SELECT DATE_FORMAT(m1, '%a %d %M') AS day
    FROM (
        SELECT SUBDATE( NOW() , INTERVAL 30 DAY) + INTERVAL m DAY AS m1
        FROM (
            select @rownum:=@rownum+1 as m from
            (select 1 union select 2 union select 3 union select 4) t1,
            (select 1 union select 2 union select 3 union select 4) t2,
            (select 1 union select 2 union select 3 union select 4) t3,
            (select 1 union select 2 union select 3 union select 4) t4,
            (select @rownum:=-1) t0
            ) d1
    ) d2 
    WHERE m1 <= now()
    ORDER BY m1
) calendar
LEFT JOIN 
(
    SELECT date_format(created_at,'%a %d %M') AS day, COUNT(*) AS nb_created
      FROM users
     WHERE datediff (now(),created_at) <=30
     GROUP BY day
) 
daily_registrations
ON calendar.day = daily_registrations.day