mysql - 平均每天创建的行数？

Question

示例表结构：

+-------------------------+---------------+------+-----+-----------------------+-----------------------------+
| Field                   | Type          | Null | Key | Default               | Extra                       |
+-------------------------+---------------+------+-----+-----------------------+-----------------------------+
| id                      | char(25)      | NO   | PRI | NULL                  |                             |
| created_at              | timestamp     | NO   |     | CURRENT_TIMESTAMP     | on update CURRENT_TIMESTAMP |
+-------------------------+---------------+------+-----+-----------------------+-----------------------------+

如何找出每天添加的平均行数？

Answer 1

这将返回一个int数字：

select count(*) / count(distinct date(created_at))
from your_table

要获取decimal数字，请使用：

select count(*) * 1.0 / count(distinct date(created_at))
from your_table

Answer 2

SELECT AVG(rowsPerDay) AS avgPerDay
FROM ( SELECT 
         COUNT(*) AS rowsPerDay
       FROM tbl
       GROUP BY DATE(created_at)
     ) AS a
;

Answer 3

如果有天数为 0 行，这些都不起作用，对吗？我想如果您每天都需要，您可以计算自第一天以来的天数并使用它

这适用于 MariaDB：

SELECT COUNT(*) / DATEDIFF ( CURRENT_DATE() , MIN(DATE(created_at)) ) AS "Avg. rows per day" 
FROM your_table;