我想写一个mysql函数。。。但我得到的语法错误是
错误1064（42000）：您的sql语法有错误；查看与您的mysql服务器版本对应的手册，以获得正确的语法来使用'）；
我的代码如下，

delimiter //
CREATE FUNCTION calculateNetItemStandardDiscountAmount(productId INT,quantity INT) RETURNS DOUBLE 
BEGIN
   DECLARE discountPer DOUBLE;
   DECLARE unitPrice DOUBLE;
   DECLARE netItemDiscountAmount DOUBLE;
   DECLARE netItemAmount DOUBLE;

   SELECT `SellingUnitPrice` into unitPrice 
   FROM `TBL_PRODUCT_MASTER` 
   WHERE `Id` = productId;
   SET netItemAmount = quantity * unitPrice ;
   insert into debugtable select concat('ACTUAL AMOUNT ', netItemAmount);

   SELECT discDetail.`DiscountPercentage` into discountPer 
   FROM `TBL_DISCOUNT_DETAIL` AS discDetail , `TBL_DISCOUNT` AS disc, TBL_PRODUCT_DISCOUNT AS prodDisc 
   WHERE disc.`DiscountStartDate` < NOW() 
         AND disc.`DiscountEndDate` > NOW() 
         AND disc.`SchemeType` = 'AMOUNT' 
         AND discDetail.DiscountId = disc.Id 
         AND prodDisc.productId = productId 
         AND prodDisc.discountId = disc.Id 
         AND prodDisc.`IsEnabled` = 1 
         AND disc.`IsEnabled` = 1 
         AND (quantity * unitPrice) >= discDetail.LowerLimit and (quantity * unitPrice) <= discDetail.HigherLimit);

   insert into debugtable select concat('STD DISCOUNT PER BY AMOUNT ', discountPer);
   IF (discountPer IS NOT NULL) THEN
       SET netItemDiscountAmount = ((netItemAmount) * (discountPer * 0.01));
       insert into debugtable select concat('APPLY VOLUME DISCOUNT ', netItemDiscountAmount);
   END IF;

   SELECT discDetail.`DiscountPercentage` into discountPer 
   FROM `TBL_DISCOUNT_DETAIL` AS discDetail , `TBL_DISCOUNT` AS disc, TBL_PRODUCT_DISCOUNT AS prodDisc 
   WHERE disc.`DiscountStartDate` < NOW() 
         AND disc.`DiscountEndDate` > NOW() 
         AND disc.`SchemeType` = 'VOLUME' 
         AND discDetail.DiscountId = disc.Id AND prodDisc.productId = productId 
         AND prodDisc.discountId = disc.Id 
         AND prodDisc.`IsEnabled` = 1  
         AND disc.`IsEnabled` = 1 
         AND (Quantity >= discDetail.LowerLimit and Quantity <= discDetail.HigherLimit);

   insert into debugtable select concat('STD DISCOUNT PER BY VOLUME ', discountPer);
   IF (discountPer IS NOT NULL) THEN
       SET netItemDiscountAmount = netItemDiscountAmount + ((netItemAmount) * (discountPer * 0.01));
       insert into debugtable select concat('APPLY AMOUNT DISCOUNT ', netItemDiscountAmount);
   END IF;

   RETURN netItemDiscountAmount;
END//
delimiter ;

任何帮助都将不胜感激。。。提前谢谢。。。