Prevent redundant results in SQL query

My query to find time clash works like this -

create table dat(id int, s time(7), e time(7));

insert into dat (id,s,e) values(1,'16:00:00.0000000','18:00:00.0000000')
insert into dat (id,s,e) values(2,'15:00:00.0000000','17:00:00.0000000')
insert into dat (id,s,e) values(3,'12:00:00.0000000','15:00:00.0000000')

//data part

QUERY - 

select * from dat a, dat b

 where  a.id != b.id 

and a.s < b.e and a.e > b.s

Result -

Now the problem is that the query lists:

• in the first row, that id 1 conflicts with id 2
• and in the second row, id 2 conflicts back with id 1

I need the distinct of this query.

Try:

SELECT * from dat a, dat b 
WHERE a.id < b.id 
    AND a.s < b.e 
    AND a.e > b.s

You can avoid the duplicate pairs by setting first id to be lower than second id.