Question

所以我试图建立一个图书馆数据库，并想知道我是否可以通过使用触发器或类似方法来实现。

我有这个名为＆＃34; category＆＃34;其中包含您可以借阅的不同类别，如书籍或DVD。

根据您借出的产品类别，您可以享受不同的时间，例如可以借用3周的书籍，但dvds只允许3天。

+--------------+---------------+------+-----+---------+----------------+
| Field        | Type          | Null | Key | Default | Extra          |
+--------------+---------------+------+-----+---------+----------------+
| id           | int(11)       | NO   | PRI | NULL    | auto_increment |
| name         | varchar(100)  | NO   |     | NULL    |                |
| time_allowed | time          | NO   |     | NULL    |                |
| days_allowed | varchar(400)  | NO   |     | NULL    |                |
+--------------+---------------+------+-----+---------+----------------+

然后我有桌子＆＃34; Borrowed＆＃34;看起来像这样

+---------------+-------------------+-------+-----+----------------------+-----------------------------+
| Field         | Type              | Null  | Key | Default              | Extra                       |
+---------------+-------------------+-------+-----+----------------------+-----------------------------+
| id            | int(11)           | NO    | PRI | None                 | auto_increment              |
| item_id       | int(11)           | NO    |     | NULL                 |                             |
| date_borrowed | timestamp         | NO    |     | CURRENT_TIMESTAMP    |                             |
| return_by     | datetime          | NO    |     | None                 |                             | 
| returned      | enum('No','Yes')  | NO    |     | No                   |                             |
| borrower_id   | int(11)           | NO    |     | None                 |                             |
| time_returned | timestamp         | Yes   |     | CURRENT_TIMESTAMP    | ON UPDATE CURRENT_TIMESTAMP |
+---------------+-------------------+-------+-----+----------------------+-----------------------------+

现在我要做的是采取＆＃34; date_borrowed＆＃34;来自＆＃34; Borrowed＆＃34; +＆＃34; time_allowed＆＃34; +＆＃34; days_allowed＆＃34;来自＆＃34;类别＆＃34; table为＆＃34; return_by＆＃34;创建日期时间值。在＆＃34; Borrowed＆＃34;表

所以如果＆＃34; date_borrowed＆＃34;是＆＃34; 2016-01-01 12：00：00＆＃34;并借用DVD然后返回＆＃34; return_by＆＃34;应该是＆＃34; 2016-01-04 12：00：00＆＃34;。

这可以通过触发器来实现吗？

非常感谢任何反馈。

更新：

CREATE TABLE `borrowed` (
 `id` int(11) NOT NULL AUTO_INCREMENT,
 `item_id` int(11) DEFAULT NULL,
 `date_borrowed` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
 `return_by` datetime NOT NULL,
 `returned` enum('No','Yes') CHARACTER SET utf8 NOT NULL DEFAULT 'No',
 `borrower_id` int(11) NOT NULL,
 `time_returned` timestamp NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
 PRIMARY KEY (`id`),
 KEY `borrower_id_idx` (`borrower_id`),
 KEY `item_id_idx` (`item_id`),
 CONSTRAINT `borrowed_ibfk_1` FOREIGN KEY (`item_id`) REFERENCES `items` (`id`) ON DELETE SET NULL ON UPDATE CASCADE,
 CONSTRAINT `borrower_id` FOREIGN KEY (`borrower_id`) REFERENCES `borrower` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=13 DEFAULT CHARSET=utf8 COLLATE=utf8_bin

CREATE TABLE `category` (
 `id` int(11) NOT NULL AUTO_INCREMENT,
 `name` varchar(100) CHARACTER SET utf8 NOT NULL,
 `time_allowed` time NOT NULL,
 `days_allowed` varchar(400) COLLATE utf8_bin NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8 COLLATE=utf8_bin

CREATE TABLE `items` (
 `id` int(11) NOT NULL AUTO_INCREMENT,
 `item_name` varchar(150) CHARACTER SET utf8 NOT NULL,
 `item_uniqueid` varchar(100) CHARACTER SET utf8 NOT NULL COMMENT 'This can be a Serial Number or a ISBN number. But has to be unique for that item',
 `item_status` enum('Ok','Damaged','Broken') CHARACTER SET utf8 NOT NULL,
 `item_comment` longtext CHARACTER SET utf8,
 `item_retired` enum('No','Yes') CHARACTER SET utf8 NOT NULL DEFAULT 'No',
 `item_dop` date NOT NULL COMMENT 'item_dop = Item Date Of Purchaes',
 `item_category` int(11) NOT NULL,
 PRIMARY KEY (`id`),
 KEY `id_category_idx` (`item_category`),
 CONSTRAINT `id_category` FOREIGN KEY (`item_category`) REFERENCES `category` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=utf8 COLLATE=utf8_bin

Answer 1

假设你的time_allowed是HOUR，你的days_allowed是天数（不是字符串的varchar），这两个表是通过列relation_key和key相关联的，你可以起诉一个选择llike this

select TIMESTAMPADD(HOUR,  c.time_allowed, 
       TIMESTAMPADD( DAY ,c.days_allowed,b.date_borrowed) ) 
from Borrowed as b 
inner join catogory on b.relation_key  = c.key

Answer 2

首先，您需要为return_by列允许NULL：

ALTER TABLE `borrowed`
    ALTER `return_by` DROP DEFAULT;
ALTER TABLE `borrowed`
    CHANGE COLUMN `return_by` `return_by` DATETIME NULL AFTER `date_borrowed`;

然后为borrowed表创建一个BEFORE INSERT触发器：

DELIMITER //
CREATE TRIGGER `borrowed_before_insert` BEFORE INSERT ON `borrowed` FOR EACH ROW BEGIN
    set new.return_by = (
        select new.date_borrowed 
            + interval c.days_allowed day
            + interval time_to_sec(c.time_allowed) second
        from items i
        join category c on c.id = i.item_category
        where i.id = new.item_id
    );
END//
DELIMITER ;

SQLFiddle-Demo

如果您更新date_borrowed列，则还需要UPDATE触发器来调整return_by值。

根据行值和时间戳计算日期

2 个答案: