MySQL Join 查询根据另一表中对应的登录ID对一个表中的字段求和

Question

I have a MySQL table comment with the following fields:

loginid submissionid points 

I have a MySQL table called submission with the following fields:

loginid submissionid

For a given submissionid , the loginid in the two tables represent different things and therefore do nor correspond.

I would like a join to sum up points by loginid . However, not by the loginid in comment , but rather the loginid in submission . The connection between the two tables is made via the submissionid

I can't get this to work. Below is what I have so far. I'm trying to get this desired sum for each loginid pulled from another, third table, which is what the l.loginid represents.

How can I do this?

LEFT JOIN (
    SELECT C2.submissionid, C2.loginid SUM(points) AS total 
    FROM comment C2
    INNER JOIN submission S2
    ON S2.submissionid = C2.submissionid
    GROUP BY C2.submissionid
) cscs ON cscs.loginid = l.loginid

Answer 1

SELECT S2.loginid, SUM(points) AS total 
FROM submission S2
INNER JOIN comment C2
ON S2.submissionid = C2.submissionid
GROUP BY S2.loginid

This will give you a points sum for each loginid in the submission table.