Postgres 10

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CREATE TABLE Tab
    (QTY int, PRICE int, VALUE int, DATE date)
;
    
INSERT INTO Tab
    (QTY, PRICE, VALUE, DATE)
VALUES
    (10, 10, 100, '2018-12-01'),
    (25, 9, 225, '2018-12-05'),
    (30, 8, 240, '2018-12-12'),
    (50, 7, 350, '2018-12-14'),
    (100, 6, 600, '2018-12-22'),
    (10, 7, 70, '2018-12-23')
;

CREATE TABLE



INSERT 0 6


select *
  ,case when cumulative_qty <= sold_qty then qty
        when sold_qty-(cumulative_qty - qty) < 0 then 0
        else sold_qty-(cumulative_qty - qty)
   end as qty_sold
  ,case when cumulative_qty <= sold_qty then qty
        when sold_qty-(cumulative_qty - qty) < 0 then 0
        else sold_qty-(cumulative_qty - qty)
   end * price as value_sold
from
 (
   select *
     ,150 as sold_qty
      -- cumulative sum of quantity in stock (FIFO)
     ,sum(qty) over (order by date rows unbounded preceding) as cumulative_qty
   from tab
 ) as dt
;


qty
price
value
date
sold_qty
cumulative_qty
qty_sold
value_sold


10
10
100
2018-12-01
150
10
10
100

25
9
225
2018-12-05
150
35
25
225

30
8
240
2018-12-12
150
65
30
240

50
7
350
2018-12-14
150
115
50
350

100
6
600
2018-12-22
150
215
35
210

10
7
70
2018-12-23
150
225
0
0



SELECT 6


select 
  sum(case when cumulative_qty <= sold_qty then qty
           when sold_qty-(cumulative_qty - qty) < 0 then 0
           else sold_qty-(cumulative_qty - qty)
      end) as qty_sold
  ,sum(case when cumulative_qty <= sold_qty then qty
            when sold_qty-(cumulative_qty - qty) < 0 then 0
            else sold_qty-(cumulative_qty - qty)
       end * price) as value_sold
from
 (
   select *
     ,150 as sold_qty
      -- cumulative sum of quantity in stock (FIFO)
     ,sum(qty) over (order by date rows unbounded preceding) as cumulative_qty
   from tab
 ) as dt


qty_sold
value_sold


150
1125



SELECT 1

qty	price	value	date	sold_qty	cumulative_qty	qty_sold	value_sold
10	10	100	2018-12-01	150	10	10	100
25	9	225	2018-12-05	150	35	25	225
30	8	240	2018-12-12	150	65	30	240
50	7	350	2018-12-14	150	115	50	350
100	6	600	2018-12-22	150	215	35	210
10	7	70	2018-12-23	150	225	0	0