mysql - 存储过程 OUT 返回空值

Question

当我尝试选择我的存储过程时，它总是返回空值。我做了一些研究，我必须指定某处输出。不确定在哪里或如何做。

delimiter $$

Create Procedure ClientPurchases (IN idClient INT, outClientAvgPurchases DECIMAL (4,2))
BEGIN 

DECLARE PurchasesAvg DECIMAL(4,2) ;

set PurchasesAvg=
(SELECT AVG(PurchaseAmount) 
FROM Purchase
inner join Client on idClient=Client_idClient);
SET outClientAvgPurchases= PurchasesAvg;

END$$


CALL ClientPurchase(3, @purchase );

SELECT  @purchase as 'Purchase Total';

Answer 1

OUT 是一个关键字，应该在参数名称之前:

Create Procedure ClientPurchases (IN idClient INT, OUT ClientAvgPurchases DECIMAL (4,2))
...
SET ClientAvgPurchases= PurchasesAvg;