MySQL 8.0

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create table Transactions (code varchar(10), qty int, date datetime primary key);
insert into Transactions values('123', 100, '2018-01-01 00:00:00');
insert into Transactions values('123', 100, '20180102');
insert into Transactions values('123', 100, '20180103');
insert into Transactions values('123', 100, '20180104');
insert into Transactions values('123', 100, '20180105');
SELECT date,
       qty, 
       (SELECT Sum(qty) 
        From   Transactions 
        Where  Transactions.date < t.date 
               AND Transactions.code = t.code) As Stock 
FROM
    Transactions t


date
qty
Stock


2018-01-01 00:00:00
100
null

2018-01-02 00:00:00
100
100

2018-01-03 00:00:00
100
200

2018-01-04 00:00:00
100
300

2018-01-05 00:00:00
100
400


ALTER TABLE Transactions t
ADD        (SELECT Sum(qty) 
        From   Transactions 
        Where  Transactions.date < t.date 
               AND Transactions.code = t.code) As Stock 
You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 't
ADD        (SELECT Sum(qty) 
        From   Transactions 
        Where  Trans' at line 1

SELECT * FROM Transactions


code
qty
date


123
100
2018-01-01 00:00:00

123
100
2018-01-02 00:00:00

123
100
2018-01-03 00:00:00

123
100
2018-01-04 00:00:00

123
100
2018-01-05 00:00:00


CREATE VIEW transactionsView
AS Select date, qty, (SELECT Sum(qty) 
        FROM   Transactions 
        WHERE  Transactions.date < t.date 
               AND Transactions.code = t.code) As Stock
From Transactions t
Select * from transactionsView


date
qty
Stock


2018-01-01 00:00:00
100
null

2018-01-02 00:00:00
100
100

2018-01-03 00:00:00
100
200

2018-01-04 00:00:00
100
300

2018-01-05 00:00:00
100
400

date	qty	Stock
2018-01-01 00:00:00	100	null
2018-01-02 00:00:00	100	100
2018-01-03 00:00:00	100	200
2018-01-04 00:00:00	100	300
2018-01-05 00:00:00	100	400