带OUT参数的MySQL存储过程

Question

I keep getting a null value when using an out parameter.

CREATE PROCEDURE `getTotalPoints`(IN `uEmail` VARCHAR(255), OUT `iTotal` DECIMAL(5,2) UNSIGNED)
begin
select
coalesce(
coalesce(sum(points_earned),0) -
coalesce(sum(points_lost),0) +
coalesce(sum(points_taken),0) -
coalesce(sum(points_traded),0),0)
from user_activities
where user_email=@uEmail into @iTotal;
end

I know the select statement works fine as without the out parameter, I get 0.00 as a result.

I'm sure it's something simple, but everything I've researched and tried has resulted in the same NULL return value.

Answer 1

Remove the " @ " symbols on the variable references.

" @uEmail " and " @iTotal " are references to user-defined variables, not the procedure arguments.

You want to reference the procedure arguments as " uEmail " and " iTotal ", without the " @ ".

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Or , you could probably get your statement to work if you did the necessary assignments to and from the user-defined variables, something like this in the body of the procedure:

-- set user-defined variable to value from procedure argument
SET @uEmail = uEmail;

-- statement references user-defined variables
SELECT ...@uEmail ... INTO @iTotal;

-- set procedure OUT argument from user-defined variable
SET iTotal = @iTotal;