Организация ограничений целостности в РСУБД

CREATE TABLE TEST ( ID SMALLINT NOT NULL, SINCE TIME NOT NULL, UNTIL TIME NOT NULL );
CREATE INDEX TEST_ID ON TEST(ID);
CREATE FUNCTION TEST_CHECK() RETURNS TRIGGER LANGUAGE PLPGSQL AS '
	DECLARE VIOLATED BOOLEAN;
	BEGIN
		LOCK TABLE TEST IN SHARE ROW EXCLUSIVE MODE;
		SELECT COUNT(*) <> 0 INTO VIOLATED
		    FROM (SELECT SUM(UNTIL-SINCE) > INTERVAL ''1 DAY'' AS OVERTIMED FROM TEST GROUP BY ID) AS T
		    WHERE OVERTIMED;
		IF VIOLATED THEN RAISE EXCEPTION ''constraint violated''; END IF;
		RETURN NULL;
	END;
';
CREATE TRIGGER TEST_CHANGE AFTER INSERT OR UPDATE ON TEST EXECUTE PROCEDURE TEST_CHECK();
INSERT INTO TEST VALUES (0, TIME '00:00:00', TIME '12:00:00'), (0, TIME '12:00:00', TIME '23:59:59');

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START TRANSACTION ISOLATION LEVEL REPEATABLE READ READ WRITE;
SELECT * FROM TEST;
-- *** вторая транзакция в это же время ***
--START TRANSACTION READ WRITE;
--INSERT INTO TEST VALUES(0, TIME '00:00:00', TIME '00:00:01');
--COMMIT;
INSERT INTO TEST VALUES(0, TIME '00:00:00', TIME '00:00:01');
COMMIT;