为什么 mysqli_insert_id() 总是返回 0?

问题描述

我有以下代码.mysqli_insert_id()(在本例中为$last_row")，它应该返回表的最后一行，总是返回 0.为什么会这样?

I have the following code. The mysqli_insert_id() (in this case "$last_row"), which is supposed to return the last row of the table, is always returning 0. Why is it so?

<?php

include 'connect-db.php';
$last_row = mysqli_insert_id($connection);

if ($content != '') {
    $sql = "INSERT INTO myCity VALUES (NULL, 'Stuttgart', 'DEU', 'Stuttgart', 617000)";

    if (!mysqli_query($connection, $sql)) {
        die('Error: ' . mysqli_error($connection));
    }

    echo $last_row;
    mysqli_close($connection);
}

推荐答案

mysqli_insert_id 确实不返回表最后一行的 ID.从文档，它:

mysqli_insert_id does not return the ID of the last row of the table. From the docs, it:

...返回对具有 AUTO_INCREMENT 属性的列的表的查询生成的 ID.如果最后一个查询不是 INSERT 或 UPDATE 语句，或者如果修改后的表没有具有 AUTO_INCREMENT 属性的列，则此函数将返回零.

...returns the ID generated by a query on a table with a column having the AUTO_INCREMENT attribute. If the last query wasn't an INSERT or UPDATE statement or if the modified table does not have a column with the AUTO_INCREMENT attribute, this function will return zero.

(我的重点)

也就是说，如果您在自动生成 ID 的插入操作之后立即运行它，那么在您进行插入操作的同一个连接上，它将返回为该插入操作生成的 ID.

That is, if you were to run it immediately after an insert that auto-generated an ID, on the same connection you did the insert with, it would return the ID generated for that insert.

上面链接的文档中的示例说明了这一点:

This is illustrated by the example in the docs linked above:

$query = "INSERT INTO myCity VALUES (NULL, 'Stuttgart', 'DEU', 'Stuttgart', 617000)";
$mysqli->query($query);

printf ("New Record has id %d.
", $mysqli->insert_id);

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