MySQL 8.0

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create table t as
     select 'emp1' as emp_name, '2021-01' as month, 10000 as salary union all
     select 'emp1' as emp_name, '2021-02' as month, 13000 as salary union all
     select 'emp1' as emp_name, '2021-03' as month, 10000 as salary union all
     select 'emp2' as emp_name, '2021-01' as month, 15000 as salary union all
     select 'emp2' as emp_name, '2021-02' as month, 15000 as salary union all
     select 'emp2' as emp_name, '2021-03' as month, 12000 as salary union all
     select 'emp3' as emp_name, '2021-01' as month, 20000 as salary union all
     select 'emp3' as emp_name, '2021-02' as month, 20000 as salary union all
     select 'emp3' as emp_name, '2021-03' as month, 13000 as salary 

Records: 9  Duplicates: 0  Warnings: 0


select emp_name, month, salary
from t
union all
select emp_name, max(month), sum(salary)
from t
group by emp_name
order by emp_name, month, salary;


emp_name
month
salary


emp1
2021-01
10000

emp1
2021-02
13000

emp1
2021-03
10000

emp1
2021-03
33000

emp2
2021-01
15000

emp2
2021-02
15000

emp2
2021-03
12000

emp2
2021-03
42000

emp3
2021-01
20000

emp3
2021-02
20000

emp3
2021-03
13000

emp3
2021-03
53000


select t.*,
       sum(salary) over (partition by emp_name order by month) as running_salary
from t;


emp_name
month
salary
running_salary


emp1
2021-01
10000
10000

emp1
2021-02
13000
23000

emp1
2021-03
10000
33000

emp2
2021-01
15000
15000

emp2
2021-02
15000
30000

emp2
2021-03
12000
42000

emp3
2021-01
20000
20000

emp3
2021-02
20000
40000

emp3
2021-03
13000
53000

emp_name	month	salary
emp1	2021-01	10000
emp1	2021-02	13000
emp1	2021-03	10000
emp1	2021-03	33000
emp2	2021-01	15000
emp2	2021-02	15000
emp2	2021-03	12000
emp2	2021-03	42000
emp3	2021-01	20000
emp3	2021-02	20000
emp3	2021-03	13000
emp3	2021-03	53000