MySQL 8.0

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create table t1 as
select 1 as id, 10 as val union all
select 1, 20 union all
select 2, 30 union all
select 3, 49
create table t2 as
select 1 as id, 10 as val union all
select 3, 20 union all
select 3, 30 union all
select 5, 49
create table t3 as
select 4 as id, 10 as val union all
select 6, 20 union all
select 2, 30 union all
select 3, 49
with u as (
  select
    id
    , val as t1_val
    , cast(null as decimal) as t2_val
    , cast(null as decimal) as t3_val
  from t1

  union all

  select
    id
    , null as t1_val
    , val as t2_val
    , null as t3_val
  from t2

  union all

  select
    id
    , null as t1_val
    , null as t2_val
    , val as t3_val
  from t3
)
select
  id
  , sum(t1_val) as t1_val
  , sum(t2_val) as t2_val
  , sum(t3_val) as t3_val
from u
group by id


id
t1_val
t2_val
t3_val


1
30
10
null

2
30
null
30

3
49
50
49

5
null
49
null

4
null
null
10

6
null
null
20

id	t1_val	t2_val	t3_val
1	30	10	null
2	30	null	30
3	49	50	49
5	null	49	null
4	null	null	10
6	null	null	20