求大神指导这样的方法怎么写，毕设毕设，活动报名

传入一个值
如果本来的参加人数总和+传入的值
select sum(usernum)from orderac where actid=1 +传入的值
大于总人数的限制

select usersnum from activity where actid=1
就不能insert into 否则能
insert into orderac(username,actid,typeid,bmtime,usernum)

 create procedure proc(in input int)
begin
    declare sum int;
    declare usernum int;
    select sum(usernum) into sum from orderac where actid=1;
    select usersnum into usernum from activity where actid=1;
    set sum = sum + 1;
    if sum <= usernum then
        insert into orderac(username,actid,typeid,bmtime,usernum)
    end if;
end;

大概是这样吧