如何在 MySQL 中生成完整的日期范围以进行用户增长分析，即使数据丢失？

在 MySQL 中获取某个范围内的所有日期，即使缺少记录

在用户数据库中，可能会遇到创建图表的需要描绘用户群的增长。使用的常见查询是：

SELECT DATE(datecreated), count(*) AS number FROM users 
WHERE DATE(datecreated) > '2009-06-21' AND DATE(datecreated) <= DATE(NOW())
GROUP BY DATE(datecreated) ORDER BY datecreated ASC

虽然此查询检索所需信息，但它忽略了没有用户注册的日期。为了解决这个问题，可以实施利用动态日历的解决方案。操作方法如下：

select  * from (
select date_add('2003-01-01 00:00:00.000', INTERVAL n5.num*10000+n4.num*1000+n3.num*100+n2.num*10+n1.num DAY ) as date from
(select 0 as num
   union all select 1
   union all select 2
   union all select 3
   union all select 4
   union all select 5
   union all select 6
   union all select 7
   union all select 8
   union all select 9) n1,
(select 0 as num
   union all select 1
   union all select 2
   union all select 3
   union all select 4
   union all select 5
   union all select 6
   union all select 7
   union all select 8
   union all select 9) n2,
(select 0 as num
   union all select 1
   union all select 2
   union all select 3
   union all select 4
   union all select 5
   union all select 6
   union all select 7
   union all select 8
   union all select 9) n3,
(select 0 as num
   union all select 1
   union all select 2
   union all select 3
   union all select 4
   union all select 5
   union all select 6
   union all select 7
   union all select 8
   union all select 9) n4,
(select 0 as num
   union all select 1
   union all select 2
   union all select 3
   union all select 4
   union all select 5
   union all select 6
   union all select 7
   union all select 8
   union all select 9) n5
) a
where date >'2011-01-02 00:00:00.000' and date < NOW()
order by date

此动态日历生成指定范围内的日期，允许将零用户基数的日期包含在结果中。通过调整日期限制并将公式应用于您的特定数据结构，您可以生成准确反映用户群增长的图表，即使在不活动期间也是如此。

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