即使我尝试了很多方法，它仍然会给我这个错误（游标或处理程序声明sql语句之后的变量或条件声明）
sp必须使用游标

CREATE PROCEDURE monthly_sum (IN cardId INT(36), IN monthN INT, OUT sumV float)
BEGIN
DECLARE cursor_1 CURSOR FOR
SELECT SUM(purchased.amountPurchased)
FROM purchased
WHERE MONTH(purchased.dateUsed) = monthN AND purchased.purchasedCardId = cardId AND DAY(purchased.dateUsed) <=10;

DECLARE cursor_2 CURSOR FOR
SELECT SUM(purchased.amountPurchased)
FROM purchased
WHERE MONTH(purchased.dateUsed)  = monthN AND purchased.purchasedCardId = cardId AND DAY(purchased.dateUsed) <=20 AND DAY(purchased.dateUsed) >10;

DECLARE cursor_3 CURSOR FOR
SELECT SUM(purchased.amountPurchased)
FROM purchased
WHERE MONTH(purchased.dateUsed) = monthN AND purchased.purchasedCardId = cardId AND DAY(purchased.dateUsed) >20;

DECLARE percentage1, percentage2, percentage3 float default 0;

OPEN cursor_1;
FETCH cursor_1
INTO percentage1;
CLOSE cursor_1;

OPEN cursor_2;
FETCH cursor_2
INTO percentage2;
CLOSE cursor_2;

OPEN cursor_3;
FETCH cursor_3
INTO percentage3;
CLOSE cursor_3;
SET sumV = percentage1*0.01 + percentage2*0.02 + percentage1*0.03;

SELECT sumV;
END

前10天预期产量的1%，后10天预期产量的2%，本月剩余天数预期产量的3%