DW Question Answer : count best answers for a user

/**
 *
 * Get user's best answers amount.
 * @see dwqa_get_the_best_answer() in the file dw-question-answer\inc\actions.php.
 * @package Customer's project.
 * @since v1.0
 * @author suifengtec
 * @license GPL V3
 * @param int:optional
 * @return int|false
 */
function dwqa_count_best_answers_for_user($user_id=false){

 $user_id=(int)$user_id;
 if(!$user_id){

 $user_id=(int)get_current_user_id();
 }

 if(!$user_id) return false;

 global $wpdb;
 $post_db=$wpdb->prefix.'posts';
 $answer_ids=$wpdb->get_results("SELECT `ID`
 FROM `{$post_db}`
 WHERE `post_type`='dwqa-answer'
 AND `post_author`={$user_id}
 ");

 if( !$answer_ids ) return false;

 $best_answer_amount=0;

 foreach($answer_ids as $answer_id){

 $question_id = get_post_meta( $answer_id->ID, '_question', true );
 $best_answer_id = dwqa_get_the_best_answer( $question_id );

 if ( $best_answer_id && $best_answer_id == $answer_id->ID ){

 $best_answer_amount++;

 }

 }

 return $best_answer_amount;

}