Postgres 12

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create table the_table (Account int, Product_A int, Product_B int, Product_C int);

CREATE TABLE


insert into the_table
values
(101, 1000, 2000, 3000),
(102, 2000, 1000, 0),
(103, 2000, 1000, 0);

INSERT 0 3


select t.account, u.product, u.qty
from the_table t
  cross join lateral ( 
     values ('A',product_a), ('B', product_b), ('C', product_c)
  ) as u(product, qty)
order by t.account;


account
product
qty


101
A
1000

101
B
2000

101
C
3000

102
A
2000

102
B
1000

102
C
0

103
A
2000

103
B
1000

103
C
0



SELECT 9

account	product	qty
101	A	1000
101	B	2000
101	C	3000
102	A	2000
102	B	1000
102	C	0
103	A	2000
103	B	1000
103	C	0