更新数据

在 Java 中更改作者姓名的示例为：

// ds is an entity of com.mysql.cj.jdbc.MysqlDataSource
try (Connection connection = ds.getConnection()) {
    PreparedStatement pstmt = connection.prepareStatement("UPDATE `authors` SET `name` = ? WHERE `id` = ?");
    pstmt.setString(1, "Helen Haruki");
    pstmt.setInt(2, 1);
    pstmt.executeUpdate();
} catch (SQLException e) {
    e.printStackTrace();
}

在 Java 中更新书籍评价的示例为：

// ds is an entity of com.mysql.cj.jdbc.MysqlDataSource

try (Connection connection = ds.getConnection()) {
    PreparedStatement p = connection.prepareStatement("INSERT INTO `ratings` (`book_id`, `user_id`, `score`, `rated_at`)
VALUES (?, ?, ?, NOW()) ON DUPLICATE KEY UPDATE `score` = ?, `rated_at` = NOW()");
    p.setInt(1, 1000);
    p.setInt(2, 1);
    p.setInt(3, 5);
    p.setInt(4, 5);
    p.executeUpdate();
} catch (SQLException e) {
    e.printStackTrace();
}

在 Java (JDBC) 中，批量更新程序类似于以下内容：

Java 代码部分：

package com.pingcap.bulkUpdate;

import com.mysql.cj.jdbc.MysqlDataSource;

import java.sql.*;
import java.util.LinkedList;
import java.util.List;
import java.util.concurrent.TimeUnit;

public class BatchUpdateExample {
    static class UpdateID {
        private Long bookID;
        private Long userID;

        public UpdateID(Long bookID, Long userID) {
            this.bookID = bookID;
            this.userID = userID;
        }

        public Long getBookID() {
            return bookID;
        }

        public void setBookID(Long bookID) {
            this.bookID = bookID;
        }

        public Long getUserID() {
            return userID;
        }

        public void setUserID(Long userID) {
            this.userID = userID;
        }

        @Override
        public String toString() {
            return "[bookID] " + bookID + ", [userID] " + userID ;
        }
    }

    public static void main(String[] args) throws InterruptedException {
        // Configure the example database connection.

        // Create a mysql data source instance.
        MysqlDataSource mysqlDataSource = new MysqlDataSource();

        // Set server name, port, database name, username and password.
        mysqlDataSource.setServerName("localhost");
        mysqlDataSource.setPortNumber(4000);
        mysqlDataSource.setDatabaseName("bookshop");
        mysqlDataSource.setUser("root");
        mysqlDataSource.setPassword("");

        UpdateID lastID = batchUpdate(mysqlDataSource, null);

        System.out.println("first time batch update success");
        while (true) {
            TimeUnit.SECONDS.sleep(1);
            lastID = batchUpdate(mysqlDataSource, lastID);
            System.out.println("batch update success, [lastID] " + lastID);
        }
    }

    public static UpdateID batchUpdate (MysqlDataSource ds, UpdateID lastID) {
        try (Connection connection = ds.getConnection()) {
            UpdateID updateID = null;

            PreparedStatement selectPs;

            if (lastID == null) {
                selectPs = connection.prepareStatement(
                        "SELECT `book_id`, `user_id` FROM `bookshop`.`ratings` " +
                        "WHERE `ten_point` != true ORDER BY `book_id`, `user_id` LIMIT 1000");
            } else {
                selectPs = connection.prepareStatement(
                        "SELECT `book_id`, `user_id` FROM `bookshop`.`ratings` "+
                            "WHERE `ten_point` != true AND `book_id` > ? AND `user_id` > ? "+
                            "ORDER BY `book_id`, `user_id` LIMIT 1000");

                selectPs.setLong(1, lastID.getBookID());
                selectPs.setLong(2, lastID.getUserID());
            }

            List<Long> idList = new LinkedList<>();
            ResultSet res = selectPs.executeQuery();
            while (res.next()) {
                updateID = new UpdateID(
                        res.getLong("book_id"),
                        res.getLong("user_id")
                );
                idList.add(updateID.getBookID());
                idList.add(updateID.getUserID());
            }

            if (idList.isEmpty()) {
                System.out.println("no data should update");
                return null;
            }

            String updateSQL = "UPDATE `bookshop`.`ratings` SET `ten_point` = true, "+
                    "`score` = `score` * 2 WHERE (`book_id`, `user_id`) IN (" +
                    placeHolder(idList.size() / 2) + ")";
            PreparedStatement updatePs = connection.prepareStatement(updateSQL);
            for (int i = 0; i < idList.size(); i++) {
                updatePs.setLong(i + 1, idList.get(i));
            }
            int count = updatePs.executeUpdate();
            System.out.println("update " + count + " data");

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

        return null;
    }

    public static String placeHolder(int n) {
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < n ; i++) {
            sb.append(i == 0 ? "(?,?)" : ",(?,?)");
        }

        return sb.toString();
    }
}

hibernate.cfg.xml 配置部分：

<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
    <session-factory>

        <!-- Database connection settings -->
        <property name="hibernate.connection.driver_class">com.mysql.cj.jdbc.Driver</property>
        <property name="hibernate.dialect">org.hibernate.dialect.TiDBDialect</property>
        <property name="hibernate.connection.url">jdbc:mysql://localhost:4000/movie</property>
        <property name="hibernate.connection.username">root</property>
        <property name="hibernate.connection.password"></property>
        <property name="hibernate.connection.autocommit">false</property>
        <property name="hibernate.jdbc.batch_size">20</property>

        <!-- Optional: Show SQL output for debugging -->
        <property name="hibernate.show_sql">true</property>
        <property name="hibernate.format_sql">true</property>
    </session-factory>
</hibernate-configuration>

每次迭代中，SELECT 按主键顺序进行查询，最多选择 1000 行未更新到 10 分制（ten_point 为 false）数据的主键值。每次 SELECT 都会选择比上一次 SELECT 结果的最大主键还要大的数据，防止重复。然后，使用批量更新的方式，对其 score 列乘 2，并且将 ten_point 设为 true，更新 ten_point 的意义是在于防止更新程序崩溃重启后，反复更新同一行数据，导致数据损坏。每次循环中的 TimeUnit.SECONDS.sleep(1); 将使得更新程序暂停 1 秒，防止批量更新程序占用过多的硬件资源。