rolling balance, MySQL

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drop table if exists amountin;

create table amountin (account varchar(255), date date,   AmountIn int);

insert into amountin values

('A',        '2017/2/6'   , 200       )
,('A',       '2017/2/5'   , 100       )
,('A',       '2017/2/5'   , 500       )
,('B',       '2017/2/1'   , 1000      )
,('B',       '2017/2/1'   ,  2000      )
,('C',     '2017/1/20'   , 25);

drop table if exists amountout;

create table amountout (account varchar(255), date date,   amountout int);

insert into amountout values

('A',        '2017/2/8'   , 200       )
,('A',       '2017/2/7'   , 100       )
,('A',       '2017/2/6'   , 500       )
,('B',       '2017/2/2'   , 1000      )
,('B',       '2017/2/1'   ,  2000      )
,('C',     '2017/1/20'   , 25);

select * 
from (
select 
@cnt := If(@prev=account , @cnt+1,1) rown, a.*,
@balance := if(  @prev=account, @balance + amountin - amountout, amountin - amountout) balance,                                                           
@prev := account prev  from 
(select account, date, amountin, 0 amountout from amountin
union all
select account, date, 0, amountout from amountout) a, (select @cnt := 1) b, (select @prev :='') c, (select @balance :=0) bal
order by account, date
    ) r
    order by account, rown desc, date desc


absolute service time: 0,34 sec