SQL Postgres union data with missed values - sql

Question

I have two results of queries:
id | col1 | col2 | col3
1 1 null 3j
2 2 12 35
3 null 32 31
4 null 43 33
5 null 44 4
id | col1 | col2 | col3
6 1 null 3j
7 2 null 35
8 3 null 31
9 4 null 33
10 5 null null
I need to do union:
id | col1 | col2 | col3
6 1 null 3j
7 2 12 35
8 3 32 31
9 4 43 33
10 5 null null
5 null 44 4
The problem is some values are missing
I wrote this big sql query to solve this problem:
select *
from (
select max(id) as id,
max(col1) as col1,
max(col2) as col2,
max(col3) as col3
from (
select max(id) as id,
max(col1) as col1,
max(col2) as col2,
max(col3) as col3
from (
select max(id) as id,
max(col1) as col1,
max(col2) as col2,
max(col3) as col3
from (
select *
from t1
where id = 1
union
select *
from t2
where id = 2
) t
group by case
when col1 is null
or
length(col1) =
0 then id
else col1 end
) t1
group by case
when col2 is null
or length(col2) = 0
then id
else col2 end
) t2
group by case
when col3 is null
or length(col3) = 0 then id
else col3 end
) t3
may be are there some ideas to simplify it? Or are there other approaches to enrich data efficiently, because I also need to do intersection, right, left, inner union and I don't want to build so monsters queries

Answer 1

well you cat try something like this:
union
select max(col1),
max(col2),
max(col3)
from t1
where id = 1
or id = 2
group by coalesce(nullif(col1, ''),
nullif(col2, ''),
nullif(col3, ''));
upd:
outer union
select max(col1),
max(col2),
max(col3)
from t1
where id = 1
or id = 2
group by coalesce(nullif(col1, ''),
nullif(col2, ''),
nullif(col3, ''))
having count = 1;
inner union
select max(col1),
max(col2),
max(col3)
from t1
where id = 1
or id = 2
group by coalesce(nullif(col1, ''),
nullif(col2, ''),
nullif(col3, ''))
having count > 1;
left and right are outer intersect with common query with 'where'