SQL：獲取與任何評論所有文章（包括0）

Question

在這一刻我有這個疑問：

select p.idpost, count(c.idpost) 
from posts p join comments c on p.idpost = c.idpost 
group by p.idpost 

結果只顯示與評論​​的帖子。我如何獲得全部的帖子？

謝謝

Answer 1

使用LEFT JOIN：

select 
    p.idpost, 
    count(c.idpost) 
from posts p 
LEFT join comments c on p.idpost = c.idpost 
group by p.idpost 

乾杯

Answer 2

使用left join代替join

select p.idpost, count(c.idpost) 
from posts p 
    left join comments c on p.idpost = c.idpost 
group by p.idpost 

Here is a good visual explanation of SQL joins with code它表明會發生什麼，每個加入