Java PreparedStatement和ON DUPLICATE KEY UPDATE:如何知道是否插入或更新了行？

Question

有下面的代码,我怎么知道execute()方法是否导致插入或更新？:

Connection c = DriverManager.getConnection(connectionString);

PreparedStatement st = c.prepareStatement("INSERT INTO `table`(`field1`) VALUES (?) ON DUPLICATE KEY UPDATE id=LAST_INSERT_ID(id);");

st.setString(1,"some value");
st.execute();

提前致谢.

Answer 1

考虑以下MySQL测试表:

CREATE TABLE `customers` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(100) NOT NULL,
  `email` varchar(100) NOT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `email` (`email`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 AUTO_INCREMENT=1 ;

现有样本数据如下:

id  name            email
--  --------------  ----------------
 1  Loblaw, Bob     bob@example.com
 2  Thompson, Gord  gord@example.com

使用默认连接设置compensateOnDuplicateKeyUpdateCounts=false(此处描述)以下Java代码

PreparedStatement ps = dbConnection.prepareStatement(
        "INSERT INTO customers (name, email) " +
        "VALUES (?, ?) " +
        "ON DUPLICATE KEY UPDATE " +
            "name = VALUES(name), " +
            "id = LAST_INSERT_ID(id)");
ps.setString(1, "McMack, Mike");
ps.setString(2, "mike@example.com");
int euReturnValue = ps.executeUpdate();
System.out.printf("executeUpdate returned %d%n", euReturnValue);
Statement s = dbConnection.createStatement();
ResultSet rs = s.executeQuery("SELECT LAST_INSERT_ID() AS n");
rs.next();
int affectedId = rs.getInt(1);
if (euReturnValue == 1) {
    System.out.printf("    => A new row was inserted: id=%d%n", affectedId);
}
else {
    System.out.printf("    => An existing row was updated: id=%d%n", affectedId);
}

生成以下控制台输出

executeUpdate returned 1
    => A new row was inserted: id=3

现在使用参数值再次运行相同的代码

ps.setString(1, "Loblaw, Robert");
ps.setString(2, "bob@example.com");

和控制台输出是

executeUpdate returned 2
    => An existing row was updated: id=1

这表明.executeUpdate如果唯一索引导致现有行更新,则实际上可以返回2.如果您需要有关实际测试代码的进一步帮助,那么您应该编辑您的问题以包含它.

编辑

进一步的测试显示,.executeUpdate如果是,将返回1

1. 尝试的INSERT被中止,因为它会导致重复的UNIQUE键值,和
2. 指定的ON DUPLICATE KEY UPDATE更改实际上不会修改现有行中的任何值.

这可以通过使用完全相同的参数值连续两次运行上述测试代码来确认.请注意,UPDATE ... id = LAST_INSERT_ID(id)"技巧"确保id返回正确的值.

如果插入的唯一值是UNIQUE键值,这可能解释了OP的测试结果.