I have the following code:

$userID = get_current_user_id();
        echo $userID;
        $sql ="
        SELECT wp_users.`user_email`,
           wp_wp_pro_quiz_statistic.`correct_count`,
           wp_wp_pro_quiz_statistic.`incorrect_count`,
           wp_wp_pro_quiz_category.`category_name`
        FROM wp_users
          INNER JOIN wp_wp_pro_quiz_statistic_ref
             ON wp_users.`ID` = wp_wp_pro_quiz_statistic_ref.`user_id`
          INNER JOIN wp_wp_pro_quiz_statistic
             ON wp_wp_pro_quiz_statistic_ref.`statistic_ref_id` = wp_wp_pro_quiz_statistic.`statistic_ref_id`
          INNER JOIN wp_wp_pro_quiz_question
             ON wp_wp_pro_quiz_statistic.`question_id` = wp_wp_pro_quiz_question.`id`
          INNER JOIN wp_wp_pro_quiz_category
             ON wp_wp_pro_quiz_question.`category_id` = wp_wp_pro_quiz_category.`category_id`
        WHERE wp_users.`ID` = $[userID]";

How can I correctly pass the current user ID into the WHERE clause?