尝试 select 数据，然后对 mariadb 中的 selected 数据进行平均

Question

SELECT 计数 FROM (SELECT COUNT(ch_id) AS 计数来自 tbl_warrants_checked WHERE status = "活动" 分组 dateChecked);

Answer 1

这使用 MariaDB 10.5，但应该适用于 ~10.2.2 之后的任何版本。

如果我们假设每天都有数据，或者我们不关心没有数据的日子，下面将计算自1个月前（最后一个月的数据）以来的平均每天检查：

-- Average of counts per day since ~1 month ago.
-- Only for days present in the set
SELECT AVG(counts) AS average
  FROM (
          SELECT COUNT(ch_id) AS counts
            FROM tbl_warrants_checked
           WHERE status = 'active'
             AND dateChecked > (current_date - INTERVAL '1' MONTH)
           GROUP BY dateChecked
       ) AS x
;

示例结果：

+---------+
| average |
+---------+
|  3.2941 |
+---------+

如果我们希望计算缺失的天数并将其视为 0，则以下生成自 1 个月前的天数和 LEFT JOIN 每天找到的天数：

-- Average of counts per day since ~1 month ago.
-- Treat missing days as 0
WITH RECURSIVE dates (date) AS (
          SELECT current_date UNION ALL
          SELECT date - INTERVAL '1' DAY FROM dates
           WHERE date > (current_date - INTERVAL '1' MONTH)
     )
SELECT AVG(COALESCE(counts, 0)) AS average
  FROM dates AS d
  LEFT JOIN (
          SELECT dateChecked
               , COUNT(ch_id) AS counts
            FROM tbl_warrants_checked
           WHERE status = 'active'
             AND dateChecked > (current_date - INTERVAL '1' MONTH)
           GROUP BY dateChecked
       ) AS x
    ON d.date = x.dateChecked
;

示例结果：

+---------+
| average |
+---------+
|  1.7500 |
+---------+

Working test case with data which produces the above results

注意：我们也可以计算缺失的天数，并在没有递归和 JOIN 的情况下将其用于最终计算。还有另一种简化方法。

尝试 select 数据，然后对 mariadb 中的 selected 数据进行平均

Trying to select data and then do a average on the selected data in mariadb

sql

xampp

mariadb