exists与count(*)

使用count(*)

SELECT count(*)
FROM actor a
JOIN film_actor fa USING (actor_id)
WHERE a.last_name = 'WAHLBERG'

执行计划

使用exists

SELECT EXISTS (
  SELECT * FROM actor a
  JOIN film_actor fa USING (actor_id)
  WHERE a.last_name = 'WAHLBERG'
)

执行计划

参考博文： https://blog.jooq.org/2016/09/14/avoid-using-count-in-sql-when-you-could-use-exists/?blogsub=confirming#subscribe-blog