php - Avoid duplication in multiple fields in SQL -

id  user_id     friend_id   134       1            2  132       2            1   82       1            5   48       1            4   28       4            1   10       6            1 

i have table of includes above details. this, need 1 row not duplicate 2 fields(user_id, friend_id).i.e in first row there user_id = 1 , friend_id = 2,and in second row user_id = 2 , friend_id = 1. don't need have both rows same values.

is possible write query following output?

id  user_id     friend_id   134       1            2   82       1            5   48       1            4   28       4            1   10       6            1 

use not exists return row if switched friendship doesn't exist - higher id (to keep 1 of pairs.)

select t1.* tablename t1 not exists (select * tablename t2                   t1.user_id = t2.friend_id                     , t1.friend_id = t1.user_id                     , t2.id > t1.id) 

and here's alternative version, influenced scaisedge (thanks!):

select * your_table  (user_id, friend_id) not in (select friend_id, user_id your_table)    or user_id > friend_id order id desc; 

the or user_id > friend_id there keep 1 instance of each pair.