MySQL 8.0

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CREATE TABLE mytable (
  id int,
  date	date,
  account int,	
  name	varchar(20),
  ending_Balance varchar(20)
);

insert into mytable values
(1, '2020-04-30',	101,	'Machine',	200),
(2, '2020-05-30',	101,	'Machine',	300),
(3, '2020-06-30',	101,	'Machine',	400),
(4, '2020-07-30',	101,	'Machine',	500);

Records: 4  Duplicates: 0  Warnings: 0


select *, lag(ending_Balance) over(partition by account order by date) as beginning_Balance
from mytable


id
date
account
name
ending_Balance
beginning_Balance


1
2020-04-30
101
Machine
200
null

2
2020-05-30
101
Machine
300
200

3
2020-06-30
101
Machine
400
300

4
2020-07-30
101
Machine
500
400


ALTER TABLE mytable ADD COLUMN beginning_Balance int;

Records: 0  Duplicates: 0  Warnings: 0


update mytable t
inner join (
  select id, lag(ending_Balance) over(partition by account order by date) as beginning_Balance
  from mytable
) as s on s.id = t.id
set t.beginning_Balance = s.beginning_Balance

Rows matched: 4  Changed: 3  Warnings: 0


select *
from mytable


id
date
account
name
ending_Balance
beginning_Balance


1
2020-04-30
101
Machine
200
null

2
2020-05-30
101
Machine
300
200

3
2020-06-30
101
Machine
400
300

4
2020-07-30
101
Machine
500
400

id	date	account	name	ending_Balance	beginning_Balance
1	2020-04-30	101	Machine	200	null
2	2020-05-30	101	Machine	300	200
3	2020-06-30	101	Machine	400	300
4	2020-07-30	101	Machine	500	400