table returning function for each row in other resultset

[Niels Jespersen]

Hello all

I have som data in a resultset. E.g: 

id date_begin date_end      amount
1  2021-01-04 2021-02-06  100
2  2021-03-17 2021-05-11  234

I have a table returning function that can take one row and split it into 
constituent monthpieces and distribute amount proportionally. 

select * from func(1, 2021-01-04, 2021-02-06, 100); 

returns 

1,2021-01-04,2021-01-31,84.848485
1,2021-02-01,2021-02-06,18.181818

So far, so good. 

Now, what I want is to run the function on the resultset from above and get 

1,2021-01-04,2021-01-31,84.848485
1,2021-02-01,2021-02-06,18.181818
2,2021-03-17,2021-03-31,63.818182
2,2021-04-01,2021-04-30,127.636364
2,2021-05-01,2021-05-11,46.8

How can I accomplish this, please. 

Regards Niels Jespersen