Retrieving Inserted Row's ID in PHP/MySQL

One of the common tasks when working with MySQL databases is inserting a row and subsequently retrieving its auto-generated ID. This process involves two distinct queries, potentially introducing a time gap between inserting the row and fetching the ID, which can lead to race conditions.

Fortunately, PHP provides a straightforward solution to this issue: the mysqli_insert_id() function. The following code demonstrates its usage:

$link = mysqli_connect('127.0.0.1', 'my_user', 'my_pass', 'my_db');
mysqli_query($link, "INSERT INTO mytable (1, 2, 3, 'blah')");
$id = mysqli_insert_id($link);

mysqli_insert_id() directly retrieves the ID generated by the most recent INSERT statement, eliminating the need for additional queries. This approach guarantees that the retrieved ID corresponds to the row just inserted.

An alternative method is to utilize MySQL's LAST_INSERT_ID() function within a single query. By combining multiple INSERT statements, it becomes possible to update several tables simultaneously and avoid the hassle of separate ID retrieval:

mysqli_query($link, "INSERT INTO my_user_table ...; INSERT INTO my_other_table (`user_id`) VALUES (LAST_INSERT_ID())");

It's crucial to note that each MySQL connection maintains its own ID sequence, preventing potential conflicts between concurrent connections.