[SQL] INSERT INTO VIEW - Replacement

[marc ratun]

Hi,
I've this data model:
CREATE SEQUENCE a_seq START 1;
CREATE SEQUENCE b_seq START 1;
CREATE TABLE a (
   aid integer NOT NULL PRIMARY KEY,
   aval character varying (255) NOT NULL
);
INSERT INTO a (select nextval('a_seq'),'a1');
INSERT INTO a (select nextval('a_seq'),'a2');
CREATE TABLE b (
   bid integer NOT NULL PRIMARY KEY,
   bval character varying (255) NOT NULL
);
INSERT INTO b (select nextval('b_seq'),'b1');
INSERT INTO b (select nextval('b_seq'),'b2');
CREATE TABLE c (
   cid integer NOT NULL,
   aid integer REFERENCES a (aid),
   bid integer REFERENCES b (bid),
   cval character varying (255) NOT NULL,
   PRIMARY KEY (cid)
);
CREATE VIEW myview AS SELECT cid,aval,bval,cval FROM c INNER JOIN a ON 
(a.aid=c.aid) INNER JOIN b ON (b.bid=c.bid);

Now I'd like to insert a row into "c" and if necessary
simultaneously create the referenced rows in
the referenced tables:
INSERT INTO myview VALUES (10,'a3','b1','c1');
(Here a row in "a" with aval 'a3' should be
created)
INSERT INTO myview VALUES (20,'a1','b2','c2');
(here a row in "a" with aval 'a1' should not
be created but referenced.)
(Same for "b").
"Insert into view" would't work, how could I do
my INSERTS efficiently in postgres without
having eache time an extra query which asks
whether there already is a row in "a" which
could be referenced to.
ie mache ich das
Thanks!
Marc
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