MySQL convert many-to-many table into one-to-one

Question

I have a table which is created by joining 2 tables and now the two columns looks like having a many-to-many relationship. I want to convert this to a one-to-one relationship meaning, values in both the columns has to be unique. Here is a sample setting;

create table Test(id1 integer, id2 integer);
insert into Test(id1, id2) values(1, 10);
insert into Test(id1, id2) values(1, 20);
insert into Test(id1, id2) values(2, 10);
insert into Test(id1, id2) values(2, 20);
select * from Test;

id1	id2
1	10
1	20
2	10
2	20

I want to convert the above table into something as below;

tbl1

id1	id2
1	10
2	20

OR

tbl2

id1	id2
1	20
2	10

How to write a SQL query to convert test table to tbl1 or tbl2 ?

Answer 1

This will take out unique values as mentioned in the comments on my other answer.

SELECT a.id1, b.id2
FROM (
    SELECT *, ROW_NUMBER() OVER (ORDER BY id1) AS RowNum FROM (SELECT DISTINCT id1 FROM test) x
) AS a,
(
    SELECT *, ROW_NUMBER() OVER (ORDER BY id2) AS RowNum FROM (SELECT DISTINCT id2 FROM test) x
) AS b
WHERE a.RowNum = b.RowNum

Let me know if there is something I misunderstood.