wpJLGJc7

1CREATE TABLE IF NOT EXISTS edges (
2   src INT NOT NULL REFERENCES nodes(id) ON UPDATE CASCADE ON DELETE CASCADE
3  ,tgt INT NOT NULL REFERENCES nodes(id) ON UPDATE CASCADE ON DELETE CASCADE
4  ,rel TEXT NOT NULL
5  ,rel_type INT NOT NULL
6  ,PRIMARY KEY (src, tgt, rel)
7  ,UNIQUE (src, tgt, rel)
8  ); 
9     
10select * from edges;
11 src | tgt |    rel    | rel_type 
12-----+-----+-----------+----------
13   1 |   2 | 5.4.2.2   |        2
14   2 |   3 | 5.3.1.9   |        2
15   ...
16   5 |   6 | 2.7.1.2   |        1
17   5 |   6 | 2.7.1.147 |        1
18   6 |   2 | 5.3.1.9   |        2
19   6 |   3 | 5.3.1.9   |        2
20   ... 
21     
22ALTER TABLE edges ADD CONSTRAINT duplicate_rel_check CHECK ((src, tgt) <> (tgt, src) WHERE rel_type = 2); 
23     
24CREATE UNIQUE INDEX ON edge ( greatest(src, tgt, rel_type=2), least(tgt, src, rel_type=2) );