How to sum the total of each row?

Question

Data is

    cases            e_id
    NULL             2820   
    3                3107   
    5                2987   
    66               2987   
    18               503
    26               503    
    1                503    
    108              503
    32               503
    4                503    

Expectation

On the basis of unique e_id , sum the cases in extreme count column.

        cases            e_id         count
        NULL             2820          0
        3                3107          3
        5                2987          71
        66               2987          71
        18               503           189
        26               503           189
        1                503           189
        108              503           189
        32               503           189
        4                503           189

Answer 1

That can be done using a window function:

select cases, e_id, sum(cases) over (partition by e_id) as count
from the_table;