How to Resolve the PHP \'Commands out of sync\' Error When Using MySQLi Prepared Statements?

PHP Commands Out of Sync Error: Causes and Resolution

When working with PHP and MySQLi to retrieve data from a database using prepared statements, you may encounter the "Commands out of sync, you can't run the command now" error. This issue typically arises when attempting to execute multiple prepared statements within the same PHP script.

The error occurs because MySQLi's query() method, when used with the MYSQLI_USE_RESULT option, leaves subsequent calls in a "stale" state. To resolve this, it's crucial to properly finish processing the results of the first statement before proceeding to the next.

One solution involves calling mysqli_free_result() after each result set has been retrieved. This function releases any pending results from the buffer, allowing subsequent statements to run successfully.

Another effective approach is to employ mysqli::next_result(). After executing each prepared statement, call next_result() to advance the internal pointer within MySQLi, ensuring proper synchronization for the next statement. This is especially relevant when working with stored procedures or multiple result sets.

Here's an example demonstrating the use of next_result():

<?php

$mysqli = new mysqli('localhost', 'user', 'password', 'database');

// Prepare and execute first statement
$stmt1 = $mysqli->prepare("SELECT * FROM users WHERE username = ?");
$stmt1->bind_param('s', $username);
$stmt1->execute();
$stmt1->store_result();

// Free the result set and advance to the next result
$stmt1->free_result();
$mysqli->next_result();

// Prepare and execute second statement
$stmt2 = $mysqli->prepare("SELECT * FROM orders WHERE user_id = ?");
$stmt2->bind_param('i', $userId);
$stmt2->execute();
$stmt2->store_result();

// Bind results and fetch data
$stmt2->bind_result($orderId, $productId, $quantity);
while ($stmt2->fetch()) {
    // Do something with the fetched data
}

$stmt2->free_result();
$mysqli->close();

?>

By implementing these strategies, you can avoid the "Commands out of sync" error and ensure smooth execution of multiple prepared statements in your PHP scripts.

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