Postgres 9.5

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create table t (id int, v1 int, v2 int, v3 int);
insert into t values
(1, 10, 3, null),
(2, 5,null,1 ),
(3, null,2, 7 );

3 rows affected

SELECT *
FROM t


id
v1
v2
v3


1
10
3
null

2
5
null
1

3
null
2
7


with base as (
SELECT id,
jsonb_agg(jsonb_build_object('v1',v1,'v2',v2,'v3',v3)) as j
from t
group by id
)
SELECT id
,x->'v1' as v1
FROM base
,jsonb_array_elements(j) t(x)


id
v1


1
10

3
null

2
5

id	v1	v2	v3
1	10	3	null
2	5	null	1
3	null	2	7