Why Do I Get \'Commands out of sync\' Errors When Using Multiple PHP MySQLi Prepared Statements?

PHP Commands Out of Sync: Resolving the Error in Multiple Prepared Statement Usage

In PHP, when attempting to execute multiple prepared statements using MySQLi, you may encounter the error "Commands out of sync, you can't run the command now." This error occurs due to MySQLi's default handling of result sets from queries.

One potential cause of this error is the use of MYSQLI_USE_RESULT when executing the query. This mode optimizes performance by avoiding the buffering of the entire result set. However, it requires that you manually release the result using mysqli_free_result(). If you fail to do so before executing subsequent statements, the command sequence becomes out of sync.

To resolve this issue, ensure that you call mysqli_free_result() after fetching all rows from each statement. Alternatively, you can use the store_result() method to store the entire result set in memory, allowing you to access it later without worrying about potential conflicts.

Another common cause of this error is the presence of pending results from a previous query. When executing multiple queries within a loop, ensure that you call mysqli_next_result() after processing each result set. This method releases any remaining results and prepares the connection for subsequent queries.

Here's an example of how to fix the error by calling both mysqli_free_result() and mysqli_next_result():

$stmt = $mysqli->prepare("SELECT id, username, password, firstname, lastname, salt FROM members WHERE email = ? LIMIT 1");
$stmt->bind_param('s', $loweredEmail);
$stmt->execute();
$stmt->store_result();
$stmt->bind_result($user_id, $username, $db_password, $firstname, $lastname, $salt);
$stmt->fetch();

$stmt->free_result();
$stmt->close();

while ($mysqli->more_results()) {
    $mysqli->next_result();
}

$stmt1 = $mysqli->prepare("SELECT privileges FROM delegations WHERE id = ? LIMIT 1");
$stmt1->bind_param('s', $user_id);
$stmt1->execute();
$stmt1->store_result();
$stmt1->bind_result($privileges);
$stmt1->fetch();

By properly handling result sets and releasing them when not needed, you can avoid the "Commands out of sync" error and ensure seamless execution of multiple prepared statements.

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