create procedure query(@xh char(6)=xh)
as
if not exists(select * from xsb where xh=@xh)
print '学号不存在'
else
begin
select * from(select xsb.xh,xm,kcm,cj from xsb join cjb join kcb
on cjb.kch=kcb.kch
on xsb.xh=pcjb.xh)
as temp(xh,xm,kcm,cj) where xh=@xh
end


execute query '081102'

--默认*为全部
create procedure query(@xh char(6) = '*')
as
if isnull(@xh,'*') = '*'
begin
    select xsb.xh,xsb.xm,kcb.kcm,cjb.cj 
    from xsb,cjb,kcb
    where cjb.kch = kcb.kch
    and xsb.xh = cjb.xh
end
else
begin
    select xsb.xh,xsb.xm,kcb.kcm,cjb.cj 
    from xsb,cjb,kcb
    where cjb.kch = kcb.kch
    and xsb.xh = cjb.xh
    and xsb.xh = @xh
end