On Wed, Aug 2, 2017 at 5:44 PM, John McKown <john.archie.mckown@xxxxxxxxx> wrote:
Is there a simple way to do bidirectional mapping of a table with itself? I am thinking of a "spousal" type relationship, where it is true that if A is spouse of B, then B is spouse of A. I don't necessarily want "A" and "B" to be a monogamous relationship because that is not always be true world wide. The best I can come up with so far is something like:CREATE TABLE forespouse (PERSON integer PRIMARY KEY,SPOUSE integer UNIQUECHECK( PERSON != SPOUSE) -- sorry, can't marry self);CREATE UNIQUE INDEX ON forespouse(PERSON, SPOUSE);CREATE UNIQUE INDEX ON forespouse(SPOUSE, PERSON);-- I'm not sure that the above indices are needed.CREATE VIEW backspouse AS SELECT SPOUSE, PERSON FROM forespouse;CREATE VIEW spouse ASSELECT PERSON, SPOUSE FROM forespouseUNIONSELECT SPOUSE, PERSON FROM backspouse;
Usually the way I have done this is to normalise the representation and use a table method for converting for joins. In other words:
create table marriage (party integer primary key, counterparty integer unique, check party < counterparty);
This way you can ensure that each relationship is only recorded once.
Then I would create a function that returns an array of the parties.
CREATE OR REPLACE FUNCTION parties(marriage) returns int[] language sql as
$$
select array[$1.party, $1.counterparty];
$$;
Then you can create a gin index:
create index marriage_parties_idx on marriage using gin(parties(marriage));
Then you can query on:
select ... from people p1 where first_name = 'Ashley'
join marriage m on p1 = any(marriage.parties)
--Veni, Vidi, VISA: I came, I saw, I did a little shopping.Maranatha! <><
John McKown
Best Wishes,
Chris Travers
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