如果你想在已经存在的表中添加sequence到id，你可以使用:

CREATE SEQUENCE user_id_seq;
ALTER TABLE user ALTER user_id SET DEFAULT NEXTVAL('user_id_seq');

这种方法肯定有效，我希望它能有所帮助:

CREATE TABLE fruits(
   id SERIAL PRIMARY KEY,
   name VARCHAR NOT NULL
);

INSERT INTO fruits(id,name) VALUES(DEFAULT,'apple');

or

INSERT INTO fruits VALUES(DEFAULT,'apple');

你可以在下一个链接中查看详细信息: http://www.postgresqltutorial.com/postgresql-serial/

创建序列。

CREATE SEQUENCE user_role_id_seq
  INCREMENT 1
  MINVALUE 1
  MAXVALUE 9223372036854775807
  START 3
  CACHE 1;
ALTER TABLE user_role_id_seq
  OWNER TO postgres;

和alter table

ALTER TABLE user_roles ALTER COLUMN user_role_id SET DEFAULT nextval('user_role_id_seq'::regclass);

你必须小心不要直接插入到你的SERIAL或sequence字段中，否则当序列达到插入值时，你的写入将失败:

-- Table: "test"

-- DROP TABLE test;

CREATE TABLE test
(
  "ID" SERIAL,
  "Rank" integer NOT NULL,
  "GermanHeadword" "text" [] NOT NULL,
  "PartOfSpeech" "text" NOT NULL,
  "ExampleSentence" "text" NOT NULL,
  "EnglishGloss" "text"[] NOT NULL,
  CONSTRAINT "PKey" PRIMARY KEY ("ID", "Rank")
)
WITH (
  OIDS=FALSE
);
-- ALTER TABLE test OWNER TO postgres;
 INSERT INTO test("Rank", "GermanHeadword", "PartOfSpeech", "ExampleSentence", "EnglishGloss")
           VALUES (1, '{"der", "die", "das", "den", "dem", "des"}', 'art', 'Der Mann küsst die Frau und das Kind schaut zu', '{"the", "of the" }');


 INSERT INTO test("ID", "Rank", "GermanHeadword", "PartOfSpeech", "ExampleSentence", "EnglishGloss")
           VALUES (2, 1, '{"der", "die", "das"}', 'pron', 'Das ist mein Fahrrad', '{"that", "those"}');

 INSERT INTO test("Rank", "GermanHeadword", "PartOfSpeech", "ExampleSentence", "EnglishGloss")
           VALUES (1, '{"der", "die", "das"}', 'pron', 'Die Frau, die nebenen wohnt, heißt Renate', '{"that", "who"}');

SELECT * from test; 

如果你想在已经存在的表中添加sequence到id，你可以使用:

CREATE SEQUENCE user_id_seq;
ALTER TABLE user ALTER user_id SET DEFAULT NEXTVAL('user_id_seq');

从Postgres 10开始，也支持SQL标准定义的标识列:

create table foo 
(
  id integer generated always as identity
);

创建除非明确要求否则不能重写的标识列。下面的插入将失败，因为总是生成一个列:

insert into foo (id) 
values (1);

然而，这可以被否决:

insert into foo (id) overriding system value 
values (1);

当使用默认生成的选项时，这本质上与现有的串行实现相同:

create table foo 
(
  id integer generated by default as identity
);

当手动提供值时，底层序列也需要手动调整—与串行列相同。

默认情况下，标识列不是主键(就像串行列一样)。如果应该是一个，则需要手动定义主键约束。