存储过程的输出参数是什么，帮我句子例子解释一下

随便什么数据类型都能做为参数的,之前写过一个,希望你能有用.
drop proc sp_stu
create proc sp_stu
@notpassSum int output,
@writtenpass int = 60
as
declare @writtenAvg float
select @writtenAvg=@writtenpass from stuMarks
print '本班成绩:' + convert(varchar(5),@writtenAvg)
print '------------------------------------'
select stuName,stuInfo.stuNo,writtenExam
from stuInfo inner join stuMarks
on stuInfo.stuNo = stuMarks.stuNo
where writtenExam < 60
select @notpassSum=count(stuNo) from stuMarks where writtenExam < @writtenpass

go

接下来是调用

declare @sum int
exec sp_stu @sum output,34