Limit A Table To 1 Row

Hello!

Corporate table, t1, should contain exact 1 row.
I strongly believe that there are cleaner versions
than the following combination of trigger and rule.

Thank you in advance for any improved version!

CNLIOU
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CREATE TABLE t1 (CorpId TEXT,CorpName TEXT);

CREATE FUNCTION f1() RETURNS OPAQUE AS '
DECLARE rc SMALLINT;
BEGIN SELECT COUNT(*) INTO rc FROM t1;
 IF rc > 0 THEN   RETURN NULL; END IF;
 RETURN NEW;
END;' LANGUAGE 'plpgsql';

CREATE TRIGGER trigger1 BEFORE INSERT ON t1 FOR EACH
ROW EXECUTE PROCEDURE f1();

CREATE RULE rule1 AS ON DELETE TO t1 DO INSTEAD
NOTHING;

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