数据库和表设计

-- 创建数据库
CREATE DATABASE `bank`;

-- 切换到 bank 库
USE `bank`;

-- 创建表
CREATE TABLE `user_balance` (
  `id` BIGINT UNSIGNED NOT NULL AUTO_INCREMENT ,
  `name` VARCHAR(45) NOT NULL ,
  `balance` BIGINT NOT NULL ,
  PRIMARY KEY (`id`)
)
ENGINE = InnoDB
DEFAULT CHARACTER SET = utf8mb4
COLLATE = utf8mb4_general_ci;

在 user_balance 表中准备两条数据：

mysql> select * from user_balance;
+----+--------+---------+
| id | name   | balance |
+----+--------+---------+
|  1 | letian |    1000 |
|  2 | xiaosi |    1001 |
+----+--------+---------+
2 rows in set (0.00 sec)

使用 JDBC PreparedStatement 更新和修改数据

package demo;

import java.sql.*;

/**
 * 使用 PreparedStatement 更新(修改)和删除数据
 */
public class PreparedStatementUpdateAndDelete {

    private static final String USER = "root";
    private static final String PASSWORD = "123456";

    private static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";
    private static final String DB_URL = "jdbc:mysql://127.0.0.1:3306/bank";

    public static void update(String name, Long balance) throws ClassNotFoundException, SQLException {
        Class.forName(JDBC_DRIVER);
        Connection conn =  DriverManager.getConnection(DB_URL, USER, PASSWORD);
        PreparedStatement pstmt = null;
        try {
            pstmt = conn.prepareStatement("UPDATE user_balance SET balance=? WHERE name=?");
            pstmt.setLong(1, balance);
            pstmt.setString(2, name);
            int affectRowsNum = pstmt.executeUpdate();
            System.out.println("影响的行数：" + affectRowsNum);
        } finally {
            if (pstmt != null) {
                pstmt.close();
            }
            conn.close();
        }
    }

    public static void delete(String name) throws ClassNotFoundException, SQLException {
        Class.forName(JDBC_DRIVER);
        Connection conn =  DriverManager.getConnection(DB_URL, USER, PASSWORD);
        PreparedStatement pstmt = null;
        try {
            pstmt = conn.prepareStatement("DELETE FROM user_balance where name=?");
            pstmt.setString(1, name);
            int affectRowsNum = pstmt.executeUpdate();
            System.out.println("影响的行数：" + affectRowsNum);
        } finally {
            if (pstmt != null) {
                pstmt.close();
            }
            conn.close();
        }
    }


    public static void main(String[] args) throws SQLException, ClassNotFoundException {
        update("letian", 1002L);
        delete("xiaosi");
    }
}

执行结果：

影响的行数：1
影响的行数：1

查看 user_balance表中内容：

mysql> select * from user_balance;
+----+--------+---------+
| id | name   | balance |
+----+--------+---------+
|  1 | letian |    1002 |
+----+--------+---------+
1 row in set (0.00 sec)

可以看到 name 为 xiaosi 的记录被删掉了。name 为 letian 的记录的balance变成了1002。

安全地更新和删除数据

数据库和表设计

使用 JDBC PreparedStatement 更新和修改数据