mysql - 存储过程中的神秘运行时错误

Question

DELIMITER //
drop procedure if exists stugrade//
create procedure stugrade()
begin
declare v_pid,v_sub1,v_sub2,v_sub3 int;
declare total int default 0;
declare v_finished int default 0;
declare per decimal(10,2);
declare stud_cur cursor for select sid,sub1,sub2,sub3 from student;
declare continue handler for not found set v_finished=1;
    set per=0;
open stud_cur;
label1:loop
fetch stud_cur into v_pid,v_sub1,v_sub2,v_sub3;
    if v_finished=1 then
    leave label1;
    end if;
set total=(v_sub1,v_sub2,v_sub3);
set per=total/3;
select concat(concat(concat('marks-->',v_sub1),v_sub2),v_sub3) as "subject wise marks";
select concat('total marks of student',total) as "total marks";
select concat('Percentage of student',per) as "percentage";
if(per>=66) then
    select concat('','Distinction') as "class";
elseif(per<66 and per>=60) then
    select concat('','first') as "class";
elseif(per<60 and per>=55) then
    select concat('','higher Second') as "class";
elseif(per<55 and per>=50) then
    select concat('','second') as "class";
elseif(per<50 and per>=40) then
    select concat('','pass') as "class";
else
    select concat('','fail') as "class";
end if;
end loop label1;
close stud_cur;
end//

proc-creation 查询被执行。但是当我调用 stugrade() 时，会出现错误 1241 (21000)。

Answer 1

在我看来，这条线导致了您的问题。

set total=(v_sub1,v_sub2,v_sub3);

MySQL 只能在这种上下文中处理标量。你可能想要

set total = v_sub1+v_sub2+v_sub3;

此外，CONCAT()将采用多个参数。也就是说，虽然这是正确的：

select concat(concat(concat('marks-->',v_sub1),v_sub2),v_sub3) as "subject wise marks";

可以改写为

select concat('marks-->',v_sub1,v_sub2,v_sub3) as "subject wise marks";

如果它更容易。