Compare a two column with the same table to remove duplicate - sql

Question

A sample table with two column and I need to compare the column 1 and column 2 to the same table records and need to remove the column 1 + column 2 = column 2+column 1.
I tried to do self join and case condition. But its not working

Answer 1

If I understand correctly, you can run a simple select like this if you have all reversed pairs in the table:
select col1, col2
from t
where col1 < col2;
If you have some singletons, then:
select col1, col2
from t
where col1 < col2 or
(col1 > col2 and
not exists (select 1
from t t2
where t2.col1 = t.col2 and
t2.col2 = t.col1
)
);

Answer 2

You can use the except operator.
"EXCEPT returns distinct rows from the left input query that aren't output by the right input query."
SELECT C1, C2 FROM table
Except
SELECT C2, C1 FROM table
Example with your given data set : dbfiddle

Answer 3

I am posting the answer based on oracle database and also the columns are string/varchar:
delete from table where rowid in (
select rowid from table
where column1 || column2 =column2 || column1 )
Feel free to provide more input and we can tweak the answer.

Answer 4

Okay. There might be a simpler way of doing this but this might work as well. {table} is to be replaced with your table name.
;with orderedtable as (select t1.col1, t1.col2, ROW_NUMBER() OVER(ORDER BY t1.col1, t1.col2 ASC) AS rownum
from (select distinct t2.col1, t2.col2 from {table} t2) as t1)
select f1.col1, f1.col2
from orderedtable f1
left join orderedtable f2 on f1.col1 = f2.col2 and f1.col2 = f2.col1 and f1.rownum < f2.rownum
where f2.rownum is null

Answer 5

The SQL below will get the reversed col1 and col2 rows:
select
distinct t2.col1,t1.col2
from
table t1
join
table t2 on t1.col1 = t2.col2 and t1.col2 = t2.col1
And when we get these reversed rows, we can except them with the left join clause, the complete SQL is:
select
t.col1,t.col2
from
table t
left join
(
select
distinct t2.col1,t1.col2
from
table t1
join
table t2 on t1.col1 = t2.col2 and t1.col2 = t2.col1
) tmp on t.col1 = tmp.col1 and t.col2 = tmp.col2
where
tmp.col1 is null
Is it clear?