Cumulative Sum of 2 Columns - postgresql

Question

I am using Postgresql 11.
I have 2 tables - txn_table and summary_table
create table txn_table(id int, txn_date timestamp, amount decimal);
create table summary_table(id int, txn_date date, day_Total decimal, Cumulative_Total decimal);
Sample data for txn_table is
insert into txn_table values (1, '2020-05-28 10:05:05', 100.00);
insert into txn_table values(2, '2020-05-28 11:45:10', 200.00);
insert into txn_table values(3, '2020-05-29 10:05:05', 300.00);
insert into txn_table values(4, '2020-05-29 12:10:01', 400.00);
I want to insert the data in summary_table like below
day_total contains sum of particular day
Cumulative_total contains cumulative sum of day_total
| id | txn_date | day_total | cumulative_total |
| --- | ------------------------ | --------- | ---------------- |
| 1 | 2020-05-28 | 300 | 300 |
| 2 | 2020-05-29 | 700 | 1000 |

Answer 1

I guess this select could solve your problem:
insert into summary_table
select row_number() over w as id
, txn_date
, day_total
, sum(day_total) over w as cumulative_total
from (
select txn_date::date as txn_date, sum(amount) as day_total
from txn_table
group by txn_date::date
) d
window w as (order by txn_date)
order by txn_date
(I worked it out in my head, didn't try. Perhaps prepare db fiddle or CTE with sample input.)

Answer 2

do following:
Add unique constraint to txn_date column of summary_table.
create table summary_table(id SERIAL PRIMARY KEY, txn_date date unique, day_total decimal, cumulative_total decimal);
if you want to ignore the duplicates. use below mentioned query
insert into summary_table(txn_date,day_total,cumulative_total)
(select txn_date, day_total, sum(day_total) over (order by txn_date) as cumulative_total from (
select txn_date::date as txn_date, sum(amount) as day_total
from txn_table
group by txn_date::date
) d
order by txn_date)
on conflict(txn_date)
do nothing;
if you want to update the duplicate values in summary_table. use below mentioned query
insert into summary_table(txn_date,day_total,cumulative_total)
(select txn_date, day_total, sum(day_total) over (order by txn_date) as cumulative_total from (
select txn_date::date as txn_date, sum(amount) as day_total
from txn_table
group by txn_date::date
) d
order by txn_date)
on conflict(txn_date)
do update set day_total=EXCLUDED.day_total,
cumulative_total=EXCLUDED.cumulative_total;