mysql - 查询需要 0.0005 秒，但是当用作子查询时，它会将选择增加到 2.+

Question

我有这个选择:

select c.nome, p.foto, c.user, p.user, p.id, p.data, p.titulo, p.youtube, pp.foto, count(DISTINCT likes.user) as likes_count, count(distinct comentarios.id) as comentarios_count, count(DISTINCT l2.user) as count2

from posts p 

join cadastro c on p.user=c.id 
left join profile_picture pp on p.user = pp.user
left join likes on likes.post = p.id
left join comentarios on comentarios.foto = p.id and comentarios.delete = 0  
left join likes l2 on l2.post = p.id and l2.user = 1

where (p.user in (select following from following where user =1 and block=0 and feed=0) or p.user=1) and p.delete='0'
group by p.id
order by p.id desc limit 15

通常需要 2.2705 秒。如果我删除 (p.user in (select following from following where user =1 and block=0 and feed=0) or p.user=1) and 它将需要 0.0018

如果我使用下面的选择，它只需要 0.0005 秒:

select following from following where user =1 and block=0 and feed=0

我的问题是，我做错了什么？第一个查询在 0.0018 中运行，第二个查询在 0.0005 = 0.0023 中运行。为什么我的全选是2.2705？这是什么逻辑？

Answer 1

时间没有问题。 IN 运算符将必须验证每个 p.user 是否存在于选择返回的 N 元素中，这自然会增加总时间。