返回上次插入的自动增量id php

我没有插入任何值，但自动记住了其中一列，如何获取最后插入的id值

我使用了echo

mysql\u insert\u id（）但我给了我“0”，这似乎不正确。
mysql\u insert\u id（）仅在将数据插入表时才起作用

数据库

创建表MyGuests(
id INT（6）无符号自动递增主键，
firstname VARCHAR（30）不为空，
lastname VARCHAR（30）不为空，
电邮VARCHAR（50），
注册日期时间戳
)
上次插入的ID:


示例（MySQLi面向对象）

您能显示更多代码吗？顺便说一句，
mysql.*
函数已被弃用；改用PDO或MySQLi。我认为您误解了它返回的内容，如果您有一个自动递增的int列类型，并且您插入了一条新记录，您可以获取最后一个插入的id。但是，如果您正在更新某个列字段中的给定行，则它不会为您提供最后一个插入的id。最后一个id仅在
插入后可用。递增一个值（即使用
UPDATE
）不会返回ID。ID也必须是主键。您可能可以使用max函数从该表中获取最大ID表单，即从表中选择max（ID）。它将仅返回主键字段的下一个值
<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDB";

// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);
// Check connection
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}

$sql = "INSERT INTO MyGuests (firstname, lastname, email)
VALUES ('John', 'Doe', 'john@example.com')";

if ($conn->query($sql) === TRUE) {
    $last_id = $conn->insert_id;
    echo "New record created successfully. Last inserted ID is: " . $last_id;
} else {
    echo "Error: " . $sql . "<br>" . $conn->error;
}

$conn->close();
?>

<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDB";

// Create connection
$conn = mysqli_connect($servername, $username, $password, $dbname);
// Check connection
if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
}

$sql = "INSERT INTO MyGuests (firstname, lastname, email)
VALUES ('John', 'Doe', 'john@example.com')";

if (mysqli_query($conn, $sql)) {
    $last_id = mysqli_insert_id($conn);
    echo "New record created successfully. Last inserted ID is: " . $last_id;
} else {
    echo "Error: " . $sql . "<br>" . mysqli_error($conn);
}

mysqli_close($conn);
?>

<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDBPDO";

try {
    $conn = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);
    // set the PDO error mode to exception
    $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    $sql = "INSERT INTO MyGuests (firstname, lastname, email)
    VALUES ('John', 'Doe', 'john@example.com')";
    // use exec() because no results are returned
    $conn->exec($sql);
    $last_id = $conn->lastInsertId();
    echo "New record created successfully. Last inserted ID is: " . $last_id;
    }
catch(PDOException $e)
    {
    echo $sql . "<br>" . $e->getMessage();
    }

$conn = null;
?>