How to Retrieve and Use the Last Inserted ID for Cross-Table Inserts in PHP?

Retrieving and Using Last Row ID for Cross-Table Insert in PHP

When performing multiple inserts across different tables, it becomes necessary to retrieve the last inserted ID from one table to use as a reference in subsequent inserts. In PHP, using the mysqli extension, this task requires a bit of understanding.

In your provided code, you attempted to directly bind the result of $mysqli->insert_id to the image field in your table1 insert statement. However, this approach is incorrect as the last inserted ID should be obtained from the previous insert statement.

To correctly retrieve and use the last inserted ID, you must first ensure that your table has an auto-incrementing field, typically named id. This field keeps track of the next available integer value to use as the primary key for new records.

Once you have an auto-incrementing field, you can use the mysqli_insert_id($conn) function to retrieve the ID of the last inserted row. Here's an example:

$username = 'user1';
$fname = 'John';
$lname = 'Doe';

// Insert into table2
$insert = "INSERT INTO table2 (username) 
VALUES (?)";

if ($stmt = $mysqli->prepare($insert)) {
    $stmt->bind_param('s', $username);
    $stmt->execute();
}

// Retrieve last inserted ID for image
$last_id = mysqli_insert_id($conn);

// Insert into table1
$insert = "INSERT INTO table1 (username, firstname, lastname, image) 
VALUES (?, ?, ?, $last_id)";

if ($stmt = $mysqli->prepare($insert)) {
    $stmt->bind_param('sss', $username, $fname, $lname);
    $stmt->execute();
}

In this corrected code, we first insert a record into table2, and then we retrieve the last inserted ID using mysqli_insert_id($conn). This ID is then used as the image field in the subsequent insert statement into table1.

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