CREATE TABLE `users` (
  `userId` int NOT NULL AUTO_INCREMENT,
  `userName` varchar(255) DEFAULT NULL,
  `password` varchar(255) DEFAULT NULL,
  `teacherId` int DEFAULT NULL,
  PRIMARY KEY (`userId`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8;

教室用户信息

CREATE TABLE `teachers` (
  `teacherId` int NOT NULL AUTO_INCREMENT,
  `userName` varchar(255) DEFAULT NULL,
  `password` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`teacherId`)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;

触发器设计

CREATE TRIGGER `user_insert`   //在users表中创建触发器
AFTER INSERT ON `users`       //后触发器
FOR EACH ROW

update num set usersNum=usersNum+1; //num表用户数加一


CREATE TRIGGER `user_delete` 
AFTER DELETE ON `users` 
FOR EACH ROW 

update num set usersNum=usersNum-1;//num用户数减一


CREATE TRIGGER `teachers_insert`  //teachers表中创建触发器
AFTER INSERT ON `teachers`  //后触发器
FOR EACH ROW 

updatenum set teachersNum=teachersNum+1;


CREATE TRIGGER `teachers_delete`
AFTER DELETE ON `teachers` 
FOR EACH ROW 

updatenum set teachersNum=teachersNum-1;

七、代码实现（部分）

连接数据库代码

public class JdbcUtil{
final String URL="jdbc:mysql://localhost:3306/hj?serverTimezone=UTC";
final String USERNAME="root";
final String PASSWORD="333";
PreparedStatementps= null;
Connection con = null;

static{
try {
Class.forName("com.mysql.cj.jdbc.Driver");
        } catch (ClassNotFoundExceptione) {
e.printStackTrace();
        }
    }
//获取数据库连接对象
public Connection getCon(){
try {
con = DriverManager.getConnection(URL,USERNAME,PASSWORD);
        } catch (SQLExceptionthrowables) {
throwables.printStackTrace();
        }
return con;
    }
//获取交通工具创建细节
public PreparedStatementcreateStatement(String sql){
try {
ps= getCon().prepareStatement(sql);
        } catch (SQLExceptionthrowables) {
throwables.printStackTrace();
        }
return ps;
    }
}

登录验证代码

if ("teacher".equals(choose)) {
//2.1 是否有该教师
result = dao1.login(userName, password);
if (result == 1) {
teacher = dao1.find_userName(userName);
request.getSession().setAttribute("teacher",teacher);
//request.getRequestDispatcher("/myweb/index.html").forward(request , response);
response.sendRedirect("/myweb/index_t.jsp");
        } else {
//request.getRequestDispatcher("/myweb/login_error.html").forward(request , response);
response.sendRedirect("/myweb/login_error.html");
        }
    } else if("user".equals(choose)){
result = dao.login(userName, password);
if (result == 1) {
//后面要拿用户id，在这通过userName遍历拿到 该user对象(应该从数据库里拿)
user = dao.find_userName(userName);
System.out.println(user.getUserName());
request.getSession().setAttribute("user",user);
//request.getRequestDispatcher("/myweb/index.html").forward(request , response);
response.sendRedirect("/myweb/index.html");
        } else {
//request.getRequestDispatcher("/myweb/login_error.html").forward(request , response);
response.sendRedirect("/myweb/login_error.html");
        }
    } else if ("admin".equals(choose)){
result = dao2.login(userName, password);
System.out.println(result);
if (result == 1) {
//后面要拿用户id，在这通过userName遍历拿到 该user对象(应该从数据库里拿)

admin = dao2.find_userName(userName);
System.out.println(admin.getAdminName());
request.getSession().setAttribute("admin",admin);
//request.getRequestDispatcher("/myweb/index.html").forward(request , response);
response.sendRedirect("/myweb/index_a.jsp");
        } else {
//request.getRequestDispatcher("/myweb/login_error.html").forward(request , response);
response.sendRedirect("/myweb/login_error.html");
        }
    }
//2.调用dao将查询验证信息推送给数据库

}