大家好，我如何检查重复输入（添加学生）和如何防止它。它说当我创建一个表时，我插入数据库的输入都是重复的，显然不是。与此相一致，如何检测和检查插入的输入是否与以前的输入重复。这是控制台中的第一个输出这是继续
这是我的密码：
主.java
import java.sql.Connection;import java.sql.DriverManager;import java.sql.PreparedStatement;//import java.sql.ResultSet;//import java.sql.SQLException;//import java.sql.Statement;
公共类主{
public static void main (String args[]) throws Exception {StudentDAO x1= new StudentDAO();x1.getConnection();x1.makeTable(); //create Tablex1.addstud("1","Yves Francisco", "2000000001","5","CpE","Male");x1.addstud("2","Lance Eco", "2000000002","5","CpE","Male");x1.addstud("3","Karlos Castillo", "2000000003","5","CpE","Male");x1.addstud("4","Glenn Bordonada", "2000000004","5","ECE","Male");x1.addstud("5","JM Enriquez", "2000000005","5","ECE","Male");x1.addstud("6","John Martinez", "2000000006","2","ECE","Male");x1.addstud("7","Timothy Tolentino", "2000000007","4","IT","Male");x1.addstud("8","Kyle Dacaymat", "2000000008","3","CpE","Male");x1.addstud("9","Dom Benedictos", "2000000009","1","IT","Male");x1.addstud("10","Lance Roque", "2000000010","1","ECE","Male");x1.addstud("11", "Vegeta", "2000000011", "1", "ME", "Male"); // added Student//x1.addstud("12", "Vegeta", "2000000011", "1", "ME", "Male"); // pang check if entered input is a duplicate of a field of studName, studNumber, etc.//x1.delstud(); // delete student//x1.updstuddb();x1.showdb();}
}
studentdao.java文件
//import java.util.*;import java.sql.Connection;import java.sql.DriverManager;import java.sql.PreparedStatement;import java.sql.ResultSet;//import java.sql.ArrayList;
公办班学生{
public static void main(String[] args) {// TODO Auto-generated method stub}public void showdb() throws Exception{try {Connection con = getConnection();String query = "SELECT *FROM studinfo;";PreparedStatement showstuddb= con.prepareStatement(query);ResultSet rs = showstuddb.executeQuery();System.out.println("Showing Database.....................");System.out.println("============================================================@ THE CONTENT OF THE DATABASE @============================================================");while (rs.next()){String idko = rs.getObject(1).toString();String ngalan = rs.getObject(2).toString();String numko=rs.getObject(3).toString();String baitang=rs.getObject(4).toString();String kurso=rs.getObject(5).toString();String kasarian=rs.getObject(6).toString();System.out.println("My ID number is: "+ idko + " Name is: " + ngalan + " Student Number is: " + numko + " Year/Level is: "+ baitang +" Course is: " + kurso + " Sex is: " + kasarian);}showstuddb.close();System.out.println("Nothing follows.....................");con.close();}catch (Exception e){System.out.println("Error on showing contents of database!!!" + e.getMessage());}}public void updstuddb () throws Exception{try {Connection con = getConnection();String query = "UPDATE studinfo SET studName=?, studNum=?, studYrLvl=?, studKors=?, studGender=? WHERE studid=?";PreparedStatement studup = con.prepareStatement(query);studup.setString(1, "Kakarot"); //This will be the replacementstudup.setString(2, "2000000020");studup.setString(3, "2");studup.setString(4, "IT");studup.setString(5, "dafq");studup.setString(6, "1");// The unique element among the content of the database which is used to determine which is to updatestudup.executeUpdate();System.out.println("THE LIST HAS BEEN UPDATED @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");studup.close();con.close();}catch (Exception e){System.out.println("Error in updating the database!!!" + e.getMessage());}}public void delstud(){try {Connection con = getConnection();String query = "DELETE FROM studinfo WHERE studid=?";PreparedStatement userdel = con.prepareStatement(query);userdel.setString(1, "12"); // To determine what to delete in the Database//userdel.setString(1, "2000000002");//userdel.setString(1, "2000000003");//userdel.setString(1, "2000000004");//userdel.setString(1, "2000000005");//userdel.setString(1, "2000000006");//userdel.setString(1, "2000000007");//userdel.setString(1, "2000000008");//userdel.setString(1, "2000000009");//userdel.setString(1, "2000000010");userdel.execute();userdel.close();System.out.println("Data is now deleted!!!");con.close();}catch (Exception e){System.out.println("Error!!!. Data is not deleted " + e.getMessage());}}public void addstud(String studid, String studName, String studNum, String studYrLvl, String studKors, String studGender) throws Exception{//String var1 = "Yves Francisco";//String num1 = "2000000001";//String num2 = "5";//String var2 = "CpE";//String var3 = "Male";try {Connection con = getConnection();PreparedStatement posted= con.prepareStatement("INSERT INTO studinfo (studid, studName, studNum, studYrLvl, studKors, studGender) VALUES (?,?,?,?,?,?)");int y=1;posted.setString(y++, studid);posted.setString(y++, studName);posted.setString(y++, studNum);posted.setString(y++, studYrLvl);posted.setString(y++, studKors);posted.setString(y++, studGender);posted.executeUpdate(); // Manipulate or Update tableposted.close();//con.close();}catch (Exception e){System.out.println("Error on adding columns!!!" + e.getMessage());}finally{System.out.println("Insert Successful!");}//FOR DUPLICATE INPUTS!!!!!!!!!!!!!!!!try{Connection con = getConnection();String query = "SELECT studName, studNum, studYrLvl, studKors, studGender FROM studinfo WHERE studName=?, studNum=?, studYrLvl=?, studKors=?, studGender=?";PreparedStatement checkdup = con.prepareStatement(query);ResultSet rs=checkdup.executeQuery();while (rs.next()){boolean dup1=rs.getObject(2).equals(studName);boolean dup2=rs.getObject(3).equals(studNum);boolean dup3=rs.getObject(4).equals(studYrLvl);boolean dup4=rs.getObject(5).equals(studKors);boolean dup5=rs.getObject(6).equals(studGender);System.out.println("The name you entered is: " + dup1 + " The student number you entered is: " + dup2 + " The Yr/Lvl you entered: " + dup3 + " The Course you entered: " + dup4 + " The Sex you entered is: " + dup5);}con.close();}catch (Exception e){System.out.println("You entered a duplicate value!!. Try Again! ");System.out.println("Take note that the entered Duplicate value is entered in the Database");System.out.println("Remove the duplicate value using delstud() method!!!");}}public void makeTable() throws Exception{try{Connection con= getConnection();PreparedStatement create = con.prepareStatement("CREATE TABLE IF NOT EXISTS studinfo (studid INT NOT NULL AUTO_INCREMENT PRIMARY KEY, studName varchar(255), studNum varchar(30), studYrLvl varchar(2), studKors varchar(30), studGender varchar(10));");create.executeUpdate();System.out.println("TABLE IS CREATED!!!~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~");create.close();con.close();}catch (Exception e){System.out.println("Error on creating table!!. Table not created!"+e.getMessage());}finally{System.out.println("Table created!");};}public Connection getConnection () throws Exception {try {String driver = "com.mysql.jdbc.Driver";String url = "jdbc:mysql://localhost:3306/mydb";String username= "root";String password = "root";Class.forName(driver);Connection conn= DriverManager.getConnection(url, username, password);System.out.println("You are now Connected!!");return conn; // Return if it is successfully connected!}catch (Exception e){System.out.println("Connection not Established!"+e.getMessage());}return null; // Return if unsuccessful}
}
1条答案
按热度按时间scyqe7ek1#
问题不是表中的重复值，问题是代码中有错误。我不会像你那样做，因为如果你使用try-catch，不管怎样，如果你的代码中有问题或错误（寻找重复的代码），它会回答你有一个重复的代码。否则，即使你有成千上万的副本，如果你没有得到一个错误，你不会得到一个副本。
不管怎样，代码中的错误是没有为checkdup prepared语句赋予任何值，应该将其更改为以下内容：
编辑
有一种简单的方法可以查找重复项，您只需计算代码中有多少重复项：
在insert语句中，还需要更改一些内容。这个
studid是一个自动递增列，因此不必将其放入insert中。应该是这样的：