使用输出参数调用存储过程

Herewith I have given the stored procedure "GetAvgOut":

在此我给出了存储过程“GetAvgOut”:

delimiter //
DROP PROCEDURE IF EXISTS GetAvgOut//
CREATE DEFINER = 'MailIntimator'@'127.0.0.1' PROCEDURE GetAvgOut(OUT average INT,IN col VARCHAR(30),IN tbl VARCHAR(30))
READS SQL DATA
COMMENT 'returns average'
BEGIN
SET @userVar = CONCAT(' SELECT AVG( ' , col , ' ) FROM ' , tbl );
PREPARE stmt FROM @userVar;
EXECUTE stmt;
END;
//
delimiter ;

I tried calling the aforeseen procedure using,

我尝试使用上述程序调用,

CALL GetAvgOut(@a,'Population','city');
SELECT @a;

"select @a" returns null. How can I get the average which is assigned to out parameter "@a"?

“select @a”返回null。如何获得分配给参数“@a”的平均值?

3 个解决方案

#1

I'm no mysql expert, but do you not need to refer to the OUT variable at any point and assign it a value?

我不是mysql专家,但你不需要在任何时候引用OUT变量并为其赋值吗?

For example as seen on http://dev.mysql.com/doc/refman/5.0/en/call.html:

例如,如http://dev.mysql.com/doc/refman/5.0/en/call.html所示:

CREATE PROCEDURE p (OUT ver_param VARCHAR(25), INOUT incr_param INT)
BEGIN
  # Set value of OUT parameter
  SELECT VERSION() INTO ver_param;
  # Increment value of INOUT parameter
  SET incr_param = incr_param + 1;
END;

HTH

Phil'

#2

you are not setting the OUT parameter in your select.

您没有在选择中设置OUT参数。

try updating your statement to:

尝试将您的声明更新为:

SET @userVar = CONCAT('SELECT AVG( ' , col , ' ) INTO average FROM ' , tbl );

#3

As @Philip mentioned, you need to set the value of the OUT variable. Combining @Josh's and @Philip's answer gives something like this

正如@Philip所提到的,您需要设置OUT变量的值。结合@Josh和@ Philip的答案给出了这样的结论

BEGIN
    SET @userVar = CONCAT(' SELECT AVG( ' , col , ' ) into @average FROM ' , tbl , ' ');
    PREPARE stmt FROM @userVar;
    EXECUTE stmt;
    set average = @average;
END

#1