java - sql删除没有错误但不要删除记录(除非我在Where子句中使用Firstname)

Question

我创建了一个删除数据库中人员姓名的方法。使用名字(where 子句)，sql 命令正在运行并成功删除记录。但是，在 sql 命令中使用“姓氏”可以工作，但不会删除记录。我输入了姓氏，在名字之前

public static void deletePerson (String lname ) {

     String  host = "jdbc:mysql://localhost/Students";
     String username = "username";
     String password = "password";
    try {
        Connection connect = DriverManager.getConnection(host, username, password);

            // this is not working, I dont know what wrong with this ione
        PreparedStatement statement = connect.prepareStatement("DELETE FROM person WHERE Lastname = ?");
        statement.setString(2, lname);
        statement.close();
        connect.close();
        System.out.println("worrrk");


          // this is the working
        //PreparedStatement statement = connect.prepareStatement("DELETE FROM person WHERE Firstname = ?");
        //statement.setString(1, fname);



    } catch (SQLExcepton e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

Answer 1

让我们看看您已采取的步骤...

您已经创建了一个 PreapredStatement，很好...

PreparedStatement statement = connect.prepareStatement("DELETE FROM person WHERE Lastname = ?");

您设置的参数值...不正确...

statement.setString(2, lname);

只有一个参数，所以应该是

statement.setString(1, lname);

您关闭了声明...

statement.close();

等等，什么？您是否打算实际对数据库“执行”某些命令？

尝试在 statement.close(); 之前插入 statement.executeUpdate()

现在我们已经介绍了这一点，让我们讨论一下您的(缺乏)资源管理...

如果 Connection connect = ... 和 connect.close() 之间出现问题，connect.close() (可能statement.close())语句永远不会被执行，使数据库资源保持打开状态，但不执行任何操作(被浪费)...

幸运的是，例如，Java 7+ 现在可以轻松管理此内容

try (Connection connect = DriverManager.getConnection(host, username, password)) {
    try (PreparedStatement statement = connect.prepareStatement("DELETE FROM person WHERE Lastname = ?")) {

        statement.setString(1, lname);
        int rowsDeleted = statement.executeUpdate();
        // You could inspect the number of rows deleted
        System.out.println("worrrk");

    }
} catch (SQLException e) {
    e.printStackTrace();
}

看看The try-with-resources Statement了解更多详情

已更新

在某些情况下，Connection 可能未设置为自动提交，因此您需要手动执行此操作，因此在 int rowsDeleted = statements.executeUpdate(); 您应该在关闭 PreparedStatement 或 `Connection

之前调用 connection.commit();

try (Connection connect = DriverManager.getConnection(host, username, password)) {
    try (PreparedStatement statement = connect.prepareStatement("DELETE FROM person WHERE Lastname = ?")) {

        statement.setString(1, lname);
        int rowsDeleted = statement.executeUpdate();
        if (!connect.getAutoCommit()) { 
            connect.commit();
        }
        // You could inspect the number of rows deleted
        System.out.println("worrrk");

    }
} catch (SQLException e) {
    e.printStackTrace();
}