Question

当我尝试选择它时，我的存储过程总是返回一个空值。我做了一些研究，我必须指定某处OUTPUT。不知道在哪里或如何做到这一点。

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

您可以将过程参数声明为IN，OUT或INOUT。

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

在http://dev.mysql.com/doc/refman/5.7/en/create-procedure.html

了解详情

Answer 2

OUT是一个应位于参数名称前面的关键字：

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

存储过程OUT返回空值

2 个答案: