Mysql 如何对两个表执行 sql 操作并从第二个表开始计算 groupid

Question

我正在尝试创建一个 Sql ，从第一个表“posts_main”获取所有数据，然后从第二个表“posts_comments”获取评论数

我尝试过:

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

请问我该怎么做？

谢谢......

Answer 1

尝试使用以下查询。

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