sql - match two of the same values in different column positions - snowflake-cloud-data-platform

Question

I am looking to join two different tables on the id, and need to extract unique names out of each table; if one table has a certain name but the other doesn't, there should be one value and one null. This should be vice versa as well.
With joins, the current output looks like this:
id name_1 name_2
1 max steph
1 max john
1 john chris
1 john chris
1 chris steph
1 chris null
1 null max
1 null null
1 tony john
1 tony max
expected output:
id name_1 name_2
1 max max
1 john john
1 chris chris
1 null steph
1 tony null
current sql:
select
table1.id,
table1.name as name_1,
table2.name as name_2
from table1
left join table2
on table1.id = table2.id
(snowflake)

Answer 1

SELECT
NVL(d1.id, d2.id) as id,
d1.name as name_1,
d2.name as name_2
FROM (
SELECT DISTINCT id,name FROM table1
) AS d1
FULL OUTER JOIN (
SELECT DISTINCT id,name FROM table2
) AS d2
ON d1.id = d2.id AND d1.name = d2.name
ORDER BY 1, (d1.name,d2.name)
This takes the distinct id,name pairs from both table, then full outer joins those sets of values. Thus if the id,name are in both they match. And if they don't match they are still keep.
So with these CTE's providing the fake data:
WITH table1(id,name) AS (
select * from values (1,'aa'),(1,'ab'),(2,'ba')
), table2(id,name) AS (
select * from values (1,'aa'),(1,'ac'),(2,'ba'),(2,'bb')
)
ID
NAME_1
NAME_2
1
aa
aa
1
ab
null
1
null
ac
2
ba
ba
2
null
bb

Answer 2

Following can be used for this -
with cte as
(
select distinct t1.id,name_1 from t1)
select distinct ifnull(t2.id,cte.id) id,
cte.name_1,
t2.name_2
from t2 full outer join cte
ON cte.id=t2.id
and cte.name_1 = t2.name_2
order by cte.name_1;
+----+--------+--------+
| ID | NAME_1 | NAME_2 |
|----+--------+--------|
| 1 | chris | chris |
| 1 | john | john |
| 1 | max | max |
| 1 | tony | NULL |
| 1 | NULL | steph |
+----+--------+--------+

Answer 3

Add a WHERE clause.
select
table1.id,
table1.name as name_1,
table2.name as name_2
from table1
left join table2
WHERE table1.name = table2.name
OR table1.name is null
OR table2.name is null
on table1.id = table2.id
If you just need a list of unique names
select distinct name from table1
union
select distinct name from table2

Answer 4

Simeons answer is the way to go since snowflake supports full outer joins. But for those of you that use a relational database that lacks support for full outer joins, and have the same issue, this approach can be an alternative:
select id,
if(instr(group_concat(tb), 1), name, NULL) name_1,
if(instr(group_concat(tb), 2), name, NULL) name_2
from(
select id, name, 1 tb from table1
union
select id, name, 2 tb from table2
) a
group by id, name
order by name
The result:
| id | name_1 | name_2 |
| --- | ------ | ------ |
| 1 | chris | chris |
| 1 | john | john |
| 1 | max | max |
| 1 | null | steph |
| 1 | tony | null |
Fake data:
CREATE TABLE table1 (
id int(11),
name varchar(50)
);
CREATE TABLE table2 (
id int(11),
name varchar(50)
);
INSERT INTO table1 VALUES
(1, 'max'),
(1, 'john'),
(1, 'chris'),
(1, 'tony');
INSERT INTO table2 VALUES
(1, 'steph'),
(1, 'john'),
(1, 'chris'),
(1, 'max');
And a dbfiddle: https://www.db-fiddle.com/f/gQ4U7hu2S2EyFEtZrapqdu/6