这是我的存储过程。我在为声明的变量赋值时遇到问题。当我执行它时，插入和更新命令工作正常，但声明变量的值保持为 0；但我在数据库中有一些价值。我怎样才能正确地做到这一点。
BEGIN
DECLARE PaidFee INT DEFAULT 0;
DECLARE DueFee INT DEFAULT 0;
DECLARE CourseFee INT DEFAULT 0;
INSERT INTO `creditdirectory`(`TypeID`, `PersonName`, `CreditBy`, `PersonID`, `ModeOfPayment`,`Details`,`Amount`,`CompanyID`)
VALUES(1,PersonName,CreditBy, AddmissionID, ModeOfPayment, 'Installment', PaidAmount,
CompanyID);
SELECT `CourseFee`,`PaidFee`,`DueFee` INTO CourseFee,PaidFee,DueFee FROM `studentcoursedetails` WHERE `ID`= CourseID;
SET PaidFee = PaidFee + PaidAmount;
SET DueFee = CourseFee - PaidFee;
IF (NextDueDate !='') THEN
UPDATE `studentcoursedetails` SET `PaidFee` = PaidFee, `DueFee` = DueFee, `DueDate` = NextDueDate WHERE `ID`= CourseID;
ELSE
UPDATE `studentcoursedetails` SET `PaidFee` = PaidFee, `DueFee` = …