MySQL：通过触发器插入后，将列增加1

所以这里是伙计们

我有四张桌子

---

我的第一个：

CREATE TABLE IF NOT EXISTS `Users` (
`Id_User` smallint(5) unsigned NOT NULL AUTO_INCREMENT,
`Firstname` varchar(20) NOT NULL,
`Lastname` varchar(20) NOT NULL,
PRIMARY KEY (`Id_User`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 AUTO_INCREMENT=1002 ;

CREATE TABLE IF NOT EXISTS `Subject` (
`PrimaryKey_Subject` varchar(4) NOT NULL,
`Subject_Name`  int(5) NOT NULL,
PRIMARY KEY (`PrimaryKey_Subject`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE IF NOT EXISTS `Register` (
`ForeignKey_User` smallint(5) unsigned NOT NULL,
`ForeignKey_Lesson` varchar(4) NOT NULL,
 PRIMARY KEY (`ForeignKey_User`,`ForeignKey_Lesson`),
 KEY `ForeignKey_User_I` (`ForeignKey_User`),
 KEY `ForeignKey_Lesson` (`ForeignKey_Lesson`)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE IF NOT EXISTS `Subject_Annex` (
`PrimaryKey_Subject` varchar(4) NOT NULL,
`Number_Registered`  int(5) NOT NULL,
PRIMARY KEY (`PrimaryKey_Subject`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

DELIMITER |
create trigger before_insert_subject_annexe
before INSERT
on Register
for each row
BEGIN
INSERT INTO Subject_Annex (PrimaryKey_Subject, Number_Registered)
VALUES (NEW.ForeignKey_Lesson,  + 1)
ON DUPLICATE KEY UPDATE
  Number_Registered=Number_Registered+1;
END;
DELIMITER |

CREATE TABLE IF NOT EXISTS `Subject_Annex` (
`PrimaryKey_Subject` varchar(4) NOT NULL,
`Number_Registered`  int(5) NOT NULL,
PRIMARY KEY (`PrimaryKey_Subject`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

它包含人民的数据

---

我的第二个：

CREATE TABLE IF NOT EXISTS `Users` (
`Id_User` smallint(5) unsigned NOT NULL AUTO_INCREMENT,
`Firstname` varchar(20) NOT NULL,
`Lastname` varchar(20) NOT NULL,
PRIMARY KEY (`Id_User`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 AUTO_INCREMENT=1002 ;

CREATE TABLE IF NOT EXISTS `Subject` (
`PrimaryKey_Subject` varchar(4) NOT NULL,
`Subject_Name`  int(5) NOT NULL,
PRIMARY KEY (`PrimaryKey_Subject`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE IF NOT EXISTS `Register` (
`ForeignKey_User` smallint(5) unsigned NOT NULL,
`ForeignKey_Lesson` varchar(4) NOT NULL,
 PRIMARY KEY (`ForeignKey_User`,`ForeignKey_Lesson`),
 KEY `ForeignKey_User_I` (`ForeignKey_User`),
 KEY `ForeignKey_Lesson` (`ForeignKey_Lesson`)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE IF NOT EXISTS `Subject_Annex` (
`PrimaryKey_Subject` varchar(4) NOT NULL,
`Number_Registered`  int(5) NOT NULL,
PRIMARY KEY (`PrimaryKey_Subject`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

DELIMITER |
create trigger before_insert_subject_annexe
before INSERT
on Register
for each row
BEGIN
INSERT INTO Subject_Annex (PrimaryKey_Subject, Number_Registered)
VALUES (NEW.ForeignKey_Lesson,  + 1)
ON DUPLICATE KEY UPDATE
  Number_Registered=Number_Registered+1;
END;
DELIMITER |

CREATE TABLE IF NOT EXISTS `Subject_Annex` (
`PrimaryKey_Subject` varchar(4) NOT NULL,
`Number_Registered`  int(5) NOT NULL,
PRIMARY KEY (`PrimaryKey_Subject`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

它包含学科名称：数学、科学、生物学等

---

我的第三个：

CREATE TABLE IF NOT EXISTS `Users` (
`Id_User` smallint(5) unsigned NOT NULL AUTO_INCREMENT,
`Firstname` varchar(20) NOT NULL,
`Lastname` varchar(20) NOT NULL,
PRIMARY KEY (`Id_User`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 AUTO_INCREMENT=1002 ;

CREATE TABLE IF NOT EXISTS `Subject` (
`PrimaryKey_Subject` varchar(4) NOT NULL,
`Subject_Name`  int(5) NOT NULL,
PRIMARY KEY (`PrimaryKey_Subject`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE IF NOT EXISTS `Register` (
`ForeignKey_User` smallint(5) unsigned NOT NULL,
`ForeignKey_Lesson` varchar(4) NOT NULL,
 PRIMARY KEY (`ForeignKey_User`,`ForeignKey_Lesson`),
 KEY `ForeignKey_User_I` (`ForeignKey_User`),
 KEY `ForeignKey_Lesson` (`ForeignKey_Lesson`)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE IF NOT EXISTS `Subject_Annex` (
`PrimaryKey_Subject` varchar(4) NOT NULL,
`Number_Registered`  int(5) NOT NULL,
PRIMARY KEY (`PrimaryKey_Subject`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

DELIMITER |
create trigger before_insert_subject_annexe
before INSERT
on Register
for each row
BEGIN
INSERT INTO Subject_Annex (PrimaryKey_Subject, Number_Registered)
VALUES (NEW.ForeignKey_Lesson,  + 1)
ON DUPLICATE KEY UPDATE
  Number_Registered=Number_Registered+1;
END;
DELIMITER |

CREATE TABLE IF NOT EXISTS `Subject_Annex` (
`PrimaryKey_Subject` varchar(4) NOT NULL,
`Number_Registered`  int(5) NOT NULL,
PRIMARY KEY (`PrimaryKey_Subject`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

这一个允许用户注册到课程

---

我的第四个：

CREATE TABLE IF NOT EXISTS `Users` (
`Id_User` smallint(5) unsigned NOT NULL AUTO_INCREMENT,
`Firstname` varchar(20) NOT NULL,
`Lastname` varchar(20) NOT NULL,
PRIMARY KEY (`Id_User`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 AUTO_INCREMENT=1002 ;

CREATE TABLE IF NOT EXISTS `Subject` (
`PrimaryKey_Subject` varchar(4) NOT NULL,
`Subject_Name`  int(5) NOT NULL,
PRIMARY KEY (`PrimaryKey_Subject`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE IF NOT EXISTS `Register` (
`ForeignKey_User` smallint(5) unsigned NOT NULL,
`ForeignKey_Lesson` varchar(4) NOT NULL,
 PRIMARY KEY (`ForeignKey_User`,`ForeignKey_Lesson`),
 KEY `ForeignKey_User_I` (`ForeignKey_User`),
 KEY `ForeignKey_Lesson` (`ForeignKey_Lesson`)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE IF NOT EXISTS `Subject_Annex` (
`PrimaryKey_Subject` varchar(4) NOT NULL,
`Number_Registered`  int(5) NOT NULL,
PRIMARY KEY (`PrimaryKey_Subject`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

DELIMITER |
create trigger before_insert_subject_annexe
before INSERT
on Register
for each row
BEGIN
INSERT INTO Subject_Annex (PrimaryKey_Subject, Number_Registered)
VALUES (NEW.ForeignKey_Lesson,  + 1)
ON DUPLICATE KEY UPDATE
  Number_Registered=Number_Registered+1;
END;
DELIMITER |

CREATE TABLE IF NOT EXISTS `Subject_Annex` (
`PrimaryKey_Subject` varchar(4) NOT NULL,
`Number_Registered`  int(5) NOT NULL,
PRIMARY KEY (`PrimaryKey_Subject`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

就在这里

如何设置触发器，使每次有人注册课程时所注册的数量增加

---

例如

我创建了一个用户：johndoe-->用户表

• 然后，我有了我的主题表，其中包含所有课程：数学、科学、生物等

现在，我可以通过注册表注册我新创建的用户到一个主题：比方说科学

现在我们有了主题附件表，它通过触发器，一旦我的用户（John Doe）链接到主题（Science），就应该能够显示注册到主题的用户数量，（这里是Science），每次有人注册这个主题，他们的人数也会增加1

---

因此，要使其简短

如何设置触发器，使每次有人注册到某个主题时增加注册的用户数

---

例如：

CREATE TABLE IF NOT EXISTS `Users` (
`Id_User` smallint(5) unsigned NOT NULL AUTO_INCREMENT,
`Firstname` varchar(20) NOT NULL,
`Lastname` varchar(20) NOT NULL,
PRIMARY KEY (`Id_User`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 AUTO_INCREMENT=1002 ;

CREATE TABLE IF NOT EXISTS `Subject` (
`PrimaryKey_Subject` varchar(4) NOT NULL,
`Subject_Name`  int(5) NOT NULL,
PRIMARY KEY (`PrimaryKey_Subject`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE IF NOT EXISTS `Register` (
`ForeignKey_User` smallint(5) unsigned NOT NULL,
`ForeignKey_Lesson` varchar(4) NOT NULL,
 PRIMARY KEY (`ForeignKey_User`,`ForeignKey_Lesson`),
 KEY `ForeignKey_User_I` (`ForeignKey_User`),
 KEY `ForeignKey_Lesson` (`ForeignKey_Lesson`)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE IF NOT EXISTS `Subject_Annex` (
`PrimaryKey_Subject` varchar(4) NOT NULL,
`Number_Registered`  int(5) NOT NULL,
PRIMARY KEY (`PrimaryKey_Subject`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

DELIMITER |
create trigger before_insert_subject_annexe
before INSERT
on Register
for each row
BEGIN
INSERT INTO Subject_Annex (PrimaryKey_Subject, Number_Registered)
VALUES (NEW.ForeignKey_Lesson,  + 1)
ON DUPLICATE KEY UPDATE
  Number_Registered=Number_Registered+1;
END;
DELIMITER |

CREATE TABLE IF NOT EXISTS `Subject_Annex` (
`PrimaryKey_Subject` varchar(4) NOT NULL,
`Number_Registered`  int(5) NOT NULL,
PRIMARY KEY (`PrimaryKey_Subject`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

• 主修科目：科学
• 注册人数：1

（其他人注册）

• 主修科目：科学
• 注册人数：2

（其他人注册）

• 主修科目：科学
• 注册人数：2

• 主修科目：数学

• 注册人数：1

---

等等。

我自己设法解决了这个问题：

CREATE TABLE IF NOT EXISTS `Users` (
`Id_User` smallint(5) unsigned NOT NULL AUTO_INCREMENT,
`Firstname` varchar(20) NOT NULL,
`Lastname` varchar(20) NOT NULL,
PRIMARY KEY (`Id_User`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 AUTO_INCREMENT=1002 ;

CREATE TABLE IF NOT EXISTS `Subject` (
`PrimaryKey_Subject` varchar(4) NOT NULL,
`Subject_Name`  int(5) NOT NULL,
PRIMARY KEY (`PrimaryKey_Subject`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE IF NOT EXISTS `Register` (
`ForeignKey_User` smallint(5) unsigned NOT NULL,
`ForeignKey_Lesson` varchar(4) NOT NULL,
 PRIMARY KEY (`ForeignKey_User`,`ForeignKey_Lesson`),
 KEY `ForeignKey_User_I` (`ForeignKey_User`),
 KEY `ForeignKey_Lesson` (`ForeignKey_Lesson`)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE IF NOT EXISTS `Subject_Annex` (
`PrimaryKey_Subject` varchar(4) NOT NULL,
`Number_Registered`  int(5) NOT NULL,
PRIMARY KEY (`PrimaryKey_Subject`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

DELIMITER |
create trigger before_insert_subject_annexe
before INSERT
on Register
for each row
BEGIN
INSERT INTO Subject_Annex (PrimaryKey_Subject, Number_Registered)
VALUES (NEW.ForeignKey_Lesson,  + 1)
ON DUPLICATE KEY UPDATE
  Number_Registered=Number_Registered+1;
END;
DELIMITER |

CREATE TABLE IF NOT EXISTS `Subject_Annex` (
`PrimaryKey_Subject` varchar(4) NOT NULL,
`Number_Registered`  int(5) NOT NULL,
PRIMARY KEY (`PrimaryKey_Subject`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

---

然后在我的主题附件表上：

CREATE TABLE IF NOT EXISTS `Users` (
`Id_User` smallint(5) unsigned NOT NULL AUTO_INCREMENT,
`Firstname` varchar(20) NOT NULL,
`Lastname` varchar(20) NOT NULL,
PRIMARY KEY (`Id_User`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 AUTO_INCREMENT=1002 ;

CREATE TABLE IF NOT EXISTS `Subject` (
`PrimaryKey_Subject` varchar(4) NOT NULL,
`Subject_Name`  int(5) NOT NULL,
PRIMARY KEY (`PrimaryKey_Subject`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE IF NOT EXISTS `Register` (
`ForeignKey_User` smallint(5) unsigned NOT NULL,
`ForeignKey_Lesson` varchar(4) NOT NULL,
 PRIMARY KEY (`ForeignKey_User`,`ForeignKey_Lesson`),
 KEY `ForeignKey_User_I` (`ForeignKey_User`),
 KEY `ForeignKey_Lesson` (`ForeignKey_Lesson`)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8;

CREATE TABLE IF NOT EXISTS `Subject_Annex` (
`PrimaryKey_Subject` varchar(4) NOT NULL,
`Number_Registered`  int(5) NOT NULL,
PRIMARY KEY (`PrimaryKey_Subject`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

DELIMITER |
create trigger before_insert_subject_annexe
before INSERT
on Register
for each row
BEGIN
INSERT INTO Subject_Annex (PrimaryKey_Subject, Number_Registered)
VALUES (NEW.ForeignKey_Lesson,  + 1)
ON DUPLICATE KEY UPDATE
  Number_Registered=Number_Registered+1;
END;
DELIMITER |

CREATE TABLE IF NOT EXISTS `Subject_Annex` (
`PrimaryKey_Subject` varchar(4) NOT NULL,
`Number_Registered`  int(5) NOT NULL,
PRIMARY KEY (`PrimaryKey_Subject`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

---

我在注册的数字上添加了一个唯一键这是错误使用触发器。如果可以使用SELECT语句或view轻松检索值（注册用户数），则无需存储该值。考虑将

Subject\u-appendment

实现为查询当前课程注册人数的视图。如果用户“未注册”，该怎么办？瞧，他们放弃这个话题了？与其创建触发器，不如关注如何使用select来获得实际注册人数。我只需添加一个DELETE，然后将值减少1非常糟糕的设计。MySQL资源使用不当。