Table "public.arc"
   Column    |  Type  | Modifiers 
-------------+--------+-----------
 from_siteid | bigint | 
 to_siteid   | bigint | 
Indexes:
    "fromto-unique" UNIQUE, btree (from_siteid, to_siteid)

--
-- Data for Name: arc; Type: TABLE DATA; Schema: public; Owner: crawler
--

COPY arc (from_siteid, to_siteid) FROM stdin;
1	2
1	3
1	4
1	5
1	6
1	1
1	7
1	8
1	9
1	10
1	11
1	12
1	13
1	14
\.


--
-- PostgreSQL database dump complete
--

Inserting 1,1 causes the following error:

SQL error:

ERROR:  duplicate key violates unique constraint "fromto-unique"

In statement:
INSERT INTO "arc" ("from_siteid", "to_siteid") VALUES ('1', '1')