How to select users that are not friends to a particular user

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PHP

MySQL

I'm trying to select users form database where users are not friends with the login user.for instance i have 20 users in my db,user1 request to be friends with 2 and 3 now i want to echo user4 to user20 in find friends of user1 without echoing user2 and user3 again because they already request to be friends,please someone should help me with the code am new to mysql.

What I have tried:

i have tryed to google it out but no solution yet