mysql - 从评论数和用户，帖子和评论表中获得所有帖子

Question

我有3个用户，帖子和评论表。用户表字段

ID，姓名，性别，电话

职位表中的字段是

POST_ID，USER_ID，职位，时间

意见表字段

ID，USER_ID，评论，post_id，时间

我想要得到这些字段的值

姓名，性别，职位，时间，计数（评论）

Answer 1

SELECT x.*, CONCAT(u.FirstName, ' ', u.LastName) as name, u.Gender as gender 
FROM (
    SELECT 
    a.id , a.post, a.date_time, a.user_id as uid, 
    COUNT(c.post_id) AS 'count' 
FROM 
    posts a 
LEFT JOIN 
    comments c ON a.id = c.post_id 
GROUP BY 
    a.id 
) x 
LEFT JOIN users u ON u.id=uid 

Answer 2

尝试为这样的：如果如果你想comments.id为空

SELECT User.name, User.gender, posts.posts, count(distinct ifnull(comments.id, 0)) as commentcount 
FROM User 
JOIN posts on user.id = posts.user_id 
JOIN comments on user.id =comments.user_id 
GROUP User.name, posts.posts 

这里0将取代性别组添加User.gender分组。