drop table if exists ttt;
    create temporary table ttt(
    id int auto_increment,
    username varchar(50),
    prepay int,
    leftprepay int not null default 0,
    totaluse int not null default 0,
    tempcol varchar(50),
    realuseprepay int not null default 0,
    PRIMARY key(id)) DEFAULT CHARSET=utf8;
    insert into ttt(username,prepay,totaluse)
    select 1,3,1
    union all select 1,2,1
    union all select 1,1,1
    union all select 2,3,8
    union all select 2,5,8;
    select from ttt;
    set @leftmoney =0;
    set @username = ‘’;
    update ttt set leftprepay = (@leftmoney:= if(username=@username ,@leftmoney,totaluse) - prepay),
    tempcol = (@username:= if(username=@username,@username,username)),
    realuseprepay=if(@leftmoney > 0 ,prepay,@leftmoney+prepay)
    order by username desc;
    select     from ttt;
    #######下面递增
    update paydetail d
    set balance = (@balance := @balance + debitmoney - CreditMoney)
    where d.rid > _rid;