默认 MySQL 值是查询的结果

Question

是否可以将列的默认值作为查询结果，从而在查询值时自动更新值？

我有一个带有成员和取消表的数据库，我希望 members.NumberOfCancellations 值自动填充为以下伪查询的结果：

从cancellations.date 少于今天31 天且cancellations.memberid 等于$phpvariable 的取消中选择所有

我知道这可以通过 php 和选择/更新脚本来完成，但我希望 phpmyadmin 可能有这个功能？

______________________________________________________________
|memberid  |   firstname  | lastname  | numberofcancellations|
______________________________________________________________
|1         |   john       | doe       | resultofquery(= 2)   |  
|2         |  Dave        | Smith     | resultofquery (=1)   |
______________________________________________________________

___________________________________
|id    |memberid  |   date    | time  | group |
___________________________________
|1     |1         |2016-04-19 | 08:00 | 1     |
|2     |2         |2016-04-18 | 13:00 | 4     |
|3     |1         |2016-04-15 | 18:00 | 3     |
_______________________________________________

Answer 1

如果您的 members 表还没有取消计数的列，则添加它：

ALTER TABLE members ADD numberofcancellations int AFTER lastname;

现在您可以使用取消计数更新members：

UPDATE members t1 LEFT JOIN
(
    SELECT memberid, COUNT(*) AS numberofcancellations
    FROM cancellations
    WHERE date BETWEEN CURDATE() - INTERVAL 30 DAY AND CURDATE()
    GROUP BY memberid
) t2
   ON t1.memberid = t2.memberid
SET t1.numberofcancellations = COALESCE(t2.numberofcancellations, 0)

您将需要运行一次此查询以最初填充新列。如果要更新单个成员，则可以在UPDATE 语句中添加WHERE 条件：

UPDATE members t1 LEFT JOIN
(
    SELECT memberid, COUNT(*) AS numberofcancellations
    FROM cancellations
    WHERE date BETWEEN CURDATE() - INTERVAL 30 DAY AND CURDATE()
    GROUP BY memberid
) t2
   ON t1.memberid = t2.memberid
SET t1.numberofcancellations = COALESCE(t2.numberofcancellations, 0)
WHERE t1.memberid = 1   -- or whatever value you want