Postgresql enforce unique two-way combination of columns

Question

I\'m trying to create a table that would enforce a unique combination of two columns of the same type - in both directions. E.g. this would be illegal:

col1          


        

Answer 1

Do you consider the intarray extension to be magic?

You'd need to use int keys for the users instead of text though...

Here's a possible solution:

create extension intarray;

create table friendz (
  from_id int,
  to_id int
);

create unique index on friendz ( sort( array[from_id, to_id ] ) );

insert into friendz values (1,2); -- good

insert into friendz values (2,1); -- bad

http://sqlfiddle.com/#!15/c84b7/1