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DROP SEQUENCE next_id;
DROP TABLE ids;
CREATE SEQUENCE next_id START -2 MINVALUE -2;
CREATE TABLE ids (
id int4,
idesc text
);
CREATE TRIGGER ids_nextid
BEFORE INSERT OR UPDATE ON ids
FOR EACH ROW
EXECUTE PROCEDURE autoinc (id, next_id);
INSERT INTO ids VALUES (0, 'first (-2 ?)');
INSERT INTO ids VALUES (null, 'second (-1 ?)');
INSERT INTO ids(idesc) VALUES ('third (1 ?!)');
SELECT * FROM ids;
UPDATE ids SET id = null, idesc = 'first: -2 --> 2'
WHERE idesc = 'first (-2 ?)';
UPDATE ids SET id = 0, idesc = 'second: -1 --> 3'
WHERE id = -1;
UPDATE ids SET id = 4, idesc = 'third: 1 --> 4'
WHERE id = 1;
SELECT * FROM ids;
SELECT 'Wasn''t it 4 ?' as nextval, nextval ('next_id') as value;
insert into ids (idesc) select textcat (idesc, '. Copy.') from ids;
SELECT * FROM ids;