mysql - 用多张表在mysql中计数

Question

我有两个表（MySQL）：

论坛：match_static_id，评论，...

匹配：static_id，…………

sql语句：

SELECT  forum.match_static_id, count(forum.comments) 'comments_no', matches.* 
from forum 
INNER JOIN matches ON forum.match_static_id = matches.static_id   
group by forum.match_static_id

即使我使用 group by，我也没有为每个匹配获得正确数量的评论（它总是乘以评论示例的数量 4 评论它返回 8）。我的 sql 错了吗？我只是想从你那里得到线索吗？

Answer 1

You should use Left join insted of inner

SELECT forum.match_static_id, count(forum.comments) 'comments_no', matches.* from matches LEFT JOIN forum ON forum.match_static_id = matches.static_id
group by forum.match_static_id