mysql for select using sum in another table

[charles07]

guys, please help

i need balance amount of fees all students has to pay. Following is the DB structure. `feepayid` is primary key for paymentstable and paymentregister & `studentid` is primary in studentstable. I have written a query for this, please evaluate the query.

please see the attachment for the db structure

SELECT d.`studentid`, SUM(a.`totalfee` - (SELECT SUM(`feeamount`) FROM `paymentstable`  WHERE a.`feepayid` = `feepayid`)) AS balancefee
FROM `studentstable` d
LEFT JOIN `paymentregister` a ON a.`studentid` = d.`studentid`
GROUP BY d.`studentid`;

[r035198x]

Explain the business rules a bit more. Which table contains the amounts that students are supposed to pay and which one contains the amounts that students actually paid?