sql union有点长，怎么才能优化一下呢？

select r.id,
       r.pid,
       r.article_id,
       r.content,
       r.user_id,
       r.user_name,
       r.create_time,
       r2.id      bellow_id,
       r2.content bellow_content,
       null       likes_num,
       'sonreply' op_type
from cms_article_comment r
         left join cms_article_comment r2 on r.pid = r2.id
where r.pid is not null
  and r.pid != ''
union
select r.id, r.pid, r.article_id, r.content,
    r.user_id, r.user_name, r.create_time,
    p.id bellow_id, p.title bellow_content,
    (select count (*) from cms_comment_like where comment_id=r.id) likes_num,
    'articlereply' op_type
from cms_article_comment r
    left join cms_article p
on r.article_id=p.id
where r.pid is null or r.pid = ''

不需要优化