使用Java将记录插入MySQL表

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我在MySQL中用一个表创建了一个数据库：
CREATE DATABASE iac_enrollment_system;
USE iac_enrollment_system;
CREATE TABLE course(
course_code CHAR(7),
course_desc VARCHAR(255) NOT NULL,
course_chair VARCHAR(255),
PRIMARY KEY(course_code)
);
我尝试使用Java插入记录：
// STEP 1: Import required packages
import java.sql.*;
import java.util.*;
public class SQLInsert {
// JDBC driver name and database URL
static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";
static final String DB_URL = "jdbc:mysql://localhost:3306/iac_enrollment_system";
// Database credentials
static final String USER = "root";
static final String PASS = "1234";
public static void main(String[] args) {
Connection conn = null;
Statement stmt = null;
Scanner scn = new Scanner(System.in);
String course_code = null, course_desc = null, course_chair = null;
try {
      // STEP 2: Register JDBC driver
      Class.forName("com.mysql.jdbc.Driver");
      // STEP 3: Open a connection
      System.out.print("\nConnecting to database...");
      conn = DriverManager.getConnection(DB_URL, USER, PASS);
      System.out.println(" SUCCESS!\n");
      // STEP 4: Ask for user input
      System.out.print("Enter course code: ");
      course_code = scn.nextLine();
      System.out.print("Enter course description: ");
      course_desc = scn.nextLine();
      System.out.print("Enter course chair: ");
      course_chair = scn.nextLine();
      // STEP 5: Excute query
      System.out.print("\nInserting records into table...");
      stmt = conn.createStatement();
      String sql = "INSERT INTO course " +
         "VALUES (course_code, course_desc, course_chair)";
      stmt.executeUpdate(sql);
      System.out.println(" SUCCESS!\n");
} catch(SQLException se) {
      se.printStackTrace();
} catch(Exception e) {
      e.printStackTrace();
} finally {
      try {
         if(stmt != null)
            conn.close();
      } catch(SQLException se) {
      }
      try {
         if(conn != null)
            conn.close();
      } catch(SQLException se) {
         se.printStackTrace();
      }
}
System.out.println("Thank you for your patronage!");
  }
}
输出似乎成功返回：

但是，当我从MySQL中选择时，插入的记录为空：

为什么插入空白记录？

解决方案:


            不，这是行不通的（不适用于真实数据）：
String sql = "INSERT INTO course " +
      "VALUES (course_code, course_desc, course_chair)";
stmt.executeUpdate(sql);
更改为：
String sql = "INSERT INTO course (course_code, course_desc, course_chair)" +
      "VALUES (?, ?, ?)";
使用该sql创建一个PreparedStatment，并使用索引插入值：
PreparedStatement preparedStatement = conn.prepareStatement(sql);
preparedStatement.setString(1, "Test");
preparedStatement.setString(2, "Test2");
preparedStatement.setString(3, "Test3");
preparedStatement.executeUpdate();

使用Java将记录插入MySQL表

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