计数列的值等于行ID

Question

我有这样的表。

id | name | desc | parent 
------------------------- 
1 | abc | def | 0 
2 | abc | def | 1 
3 | abc | def | 1 
4 | abc | def | 1 
5 | abc | def | 2 
6 | abc | def | 3 

，我需要得到的是这一点，让所有行数多少行parent同实际行的ID。而且所有的都必须按这个数量排序。

id | name | desc | parent | count 
------------------------- 
1 | abc | def | 0  | 3 
2 | abc | def | 1  | 1 
3 | abc | def | 1  | 1 
4 | abc | def | 1  | 0 
5 | abc | def | 2  | 0 
6 | abc | def | 3  | 0 

我这个结束了，但实际上它没有工作：/

select c.pocet, a.* from posts a, (select count(*) as pocet from posts b where b.parent=a.id) c 

感谢您的帮助！

Answer 1

试试这个例子。根据需要添加更多列。

select 
t.id,t.parent,coalesce(x.cnt,0) as cnt 
from t left join 
(select parent,count(*) as cnt 
from t 
group by parent) x 
on x.parent = t.id 

Fiddle

Answer 2

你实际上是接近，你只需要切换到标量子查询：

select a.*, 
    (select count(*) from posts b where b.parent=a.id) as pocet 
from posts a