Inserting Country Selection into MySQL PHP [duplicate]

PHP Snippet 1:

<?php

public static function postPreferences($selected_countries) {

    $database = DatabaseFactory::getFactory()->getConnection();

    // Get existing selections
    $sqlExisting = 'SELECT country_selection FROM user_settings WHERE user_id = :user_id';
    $queryExisting = $database->prepare($sqlExisting);
    $queryExisting->execute([
        ':user_id' => Session::get('user_id')
    ]);

    $existingSelections = null;

    if ($queryExisting->rowCount() > 0) {
        $existingSelections = $queryExisting->fetchRows(); // dont know this DatabaseFactory, just an example, expects an associative array
    }

    // Insert
    if ($existingSelections === null && is_array($selected_countries) && count($selected_countries) > 0) {
        $sqlInsert = 'INSERT INTO user_settings (user_id, country_selection)VALUES(:user_id, :country_selection)';
        $queryInsert = $database->prepare($sqlInsert);
        $queryInsert->execute([
            ':user_id' => Session::get('user_id'),
            ':country_selection' => implode(',', $country_selection)
        ]);

    // Update
    } else if (is_array($existingSelections) && count($existingSelections) === 1 && $existingSelections[0]['country_selection'] !== implode(',', $country_selection)) {
        $sqlUpdate = 'UPDATE user_settings SET country_selection = :country_selection WHERE user_id = :user_id';
        $queryUpdate = $database->prepare($sqlUpdate);
        $queryUpdate->execute([
            ':user_id' => Session::get('user_id'),
            ':country_selection' => (count($country_selection) === 0 ? null : implode(',', $country_selection))
        ]);
    }

    return true;
}