Mysql 我如何 sql 两个表并从第二个开始计算 groupid

Question

我正在尝试制作一个 Sql ，它从第一个 table "posts_main" 获取所有数据，然后从第二个 table "posts_comments"

我试过：

$sql = "SELECT * FROM posts_main, count(posts_comments.groupid)
INNER JOIN posts_comments ON posts_comments.groupid = posts_main.id
WHERE posts_main.user_id = '$user_id'
GROUP BY posts_main.id";

拜托，我该怎么做？

谢谢....

Answer 1

用子查询试试这个

SELECT posts.*,cnt FROM posts_main  
INNER JOIN (select posts_comments.groupid,count(posts_comments.groupid) as cnt
group by posts_comments.groupid)a
ON a.groupid = posts_main.id
WHERE posts_main.user_id = '$user_id'

Answer 2

试试下面的查询。

$sql = "select posts_main.*, 
(select groupid from posts_comments where groupid = posts_main.id group by groupid ) as count_group 
from posts_main 
WHERE posts_main.user_id = '$user_id' ";