在mysql中求和多行

Question

I have a mysql table name request and the request has the following fields

id mem_id amount status rtype
1   11     200     0     ph
2   12     200     0     ph
3   13     400     0     ph
4   14     200     0     ph
5   15     300     0     ph

what i wanted to do with this table is if a user insert another data and the rtype = gh and amount = 600 i want mysql to pick from the request table and sum the amount in order to get the new requested amount which is 600 like a peer to peer donation

The result can look like

id mem_id amount status rtype
1   11     200     0     ph
2   12     200     0     ph
4   14     200     0     ph

or

id mem_id amount status rtype
1   11     200     0     ph
3   13     400     0     ph

i have this query but it returns an empty result from my phpmyadmin

SELECT id, mem_id, SUM(amount), status, rtype FROM tbl_request WHERE rtype = 'ph' AND status = 0 AND amount = 6000 GROUP BY id;

please any help

Thanks in advance

Answer 1

You can do cumulative sum using a mysql variable.

SELECT 
    *
FROM
    (SELECT @var:=600) a,
    (SELECT 
        tbl_request.*,
            if((@var:=@var - amount) > 0, amount, amount + @var) as my_amount
    FROM
        tbl_request 
    WHERE
        rtype = 'ph' AND status = 0
    ORDER BY amount ASC) AS b
WHERE
    my_amount > 0

from here : https://stackoverflow.com/a/11935359/6124896