mysql 获取近一周的每天的用户的注册量

1, mysql 获取近一周的每天（不包括当天 now() 的）的用户的注册量与对应时间。其中 create_time 字段是注册的时间段（一般不修改）

SELECT
   DATE_FORMAT( create_time, '%Y%m%d' ) AS ymd,
   COUNT( * ) AS total
FROM
   user
WHERE
   user_from IN ( 1, 2, 3, 4, 5 )
   AND create_time BETWEEN SUBDATE( DATE( NOW( ) ), INTERVAL 7 DAY )
   AND DATE( NOW( ) )
GROUP BY
   ymd；

2，mysql 的 case when 使用：

多系统（多网站）统计注册量并且按照网站分类

SELECT DATE_FORMAT( create_time, '%Y%m%d' ) AS ymd,
CASE
user_from
WHEN 1 THEN
'网站1'
WHEN 2 THEN
'网站2'
END AS site,
COUNT( * ) AS total
FROM
user
WHERE
user_from IN ( 1, 2)
AND create_time BETWEEN SUBDATE( DATE( NOW( ) ), INTERVAL 7 DAY )
AND DATE( NOW( ) )
GROUP BY
ymd,
user_from;

3，MySQL 正则与 when case:

参考： https://www.cnblogs.com/clphp/p/6256207.html

Case具有两种格式。简单Case函数和Case搜索函数。
--简单Case函数
CASE sex
         WHEN '1' THEN '男'
         WHEN '2' THEN '女'
ELSE '其他' END
--Case搜索函数
CASE WHEN sex = '1' THEN '男'
         WHEN sex = '2' THEN '女'
ELSE '其他' END

这两种方式，可以实现相同的功能。简单Case函数的写法相对比较简洁，但是和Case搜索函数相比，功能方面会有些限制，比如写判断式。

我的解决实例：

SELECT
CASE WHEN
       substring_index( `name`, " ", 1 ) REGEXP '^pid:[0-9]{5}' THEN
           '123'
           END AS total
FROM   `address`;

========================= ===============================================================

问题一：前七天没有人注册，怎么办？

方法：日期写出，统计量为零

字段有 user_from（多个网），create_time（创建时间）

count(*) as total --统计注册量数量 ifnull(b.total,0)--没有注册量默认为零 NOW() 代替 '2013-06-10'

select a.count_time,ifnull(b.total,0) as total,b.user_from as site
from (
SELECT SUBDATE(DATE( '2013-06-10' ), interval 7 day) as count_time
union all
SELECT SUBDATE(DATE( '2013-06-10' ), interval 6 day) as count_time
union all
SELECT SUBDATE(DATE( '2013-06-10' ), interval 5 day) as count_time
union all
SELECT SUBDATE(DATE( '2013-06-10' ), interval 4 day) as count_time
union all
SELECT SUBDATE(DATE( '2013-06-10' ), interval 3 day) as count_time
union all
SELECT SUBDATE(DATE( '2013-06-10' ), interval 2 day) as count_time
union all
SELECT SUBDATE(DATE( '2013-06-10' ), interval 1 day) as count_time
) a left join (
select date(create_time) as datetime, count(*) as total, user_from
from fashion_user
where user_from =5
group by date(create_time)
) b on a.count_time = b.datetime;

问题二：统计的当前日期之后的日期 更多怎么办：比如 INTERVAL 7 DAY 改为 INTERVAL 1 month

创建数据库表 num：与注册统计表搭配使用

CREATE TABLE num (i int);
INSERT INTO num (i) VALUES (0), (1), (2), (3), (4), (5), (6), (7), (8), (9);

select a.count_time,COALESCE(b.total,0) total from(
SELECT ADDDATE(NOW(),c.id) as count_time
from (
select
n1.i + n10.i * 10 + n100.i * 100 AS id
from
num n1
   CROSS JOIN num AS n10
   CROSS JOIN num AS n100
   ) AS c
WHERE
ADDDATE(NOW(),c.id)<= date_add(NOW(),INTERVAL 7 DAY)) a
LEFT JOIN (SELECT left(create_time,10) as udate,count(*) total FROM fashion_user where user_from = 5 #5-网站五
GROUP BY udate) b on a.count_time = b.udate order by a.count_time;

mysql 获取近一周的每天的用户的注册量

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