PolarDB-for-PostgreSQL

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