如何将“nextval('testing_thing_thing_id_seq'::regclass)”声明为postgres表“testing_thing”中“thing_id”列的默认值？

Question

在我的 postgres 数据库中有一个名为

testing_thing

的表，我可以看到它（通过在我的 psql 提示符中运行

\d testing_thing

）它被定义为

                                        Table "public.testing_thing"

    Column    |       Type        | Collation | Nullable |                       Default                       

--------------+-------------------+-----------+----------+-----------------------------------------------------

 thing_id   | integer           |           | not null | nextval('testing_thing_thing_id_seq'::regclass)

 thing_num  | smallint          |           | not null | 0

 thing_desc | character varying |           | not null | 

Indexes:

    "testing_thing_pk" PRIMARY KEY, btree (thing_num)

我想删除它并按原样重新创建它，但我不知道如何重现

nextval('testing_thing_thing_id_seq'::regclass)

列

thing_id

的部分。

这是我用来创建表的查询：

CREATE TABLE testing_thing(
   thing_id integer NOT NULL, --what else should I put here?
   thing_num smallint NOT NULL PRIMARY KEY DEFAULT 0,
   thing_desc varchar(100) NOT NULL
);

缺少什么？

Answer 1

将

DEFAULT

添加到要递增的列并调用

nextval()

:

CREATE SEQUENCE testing_thing_thing_id_seq START WITH 1;

CREATE TABLE testing_thing(
   thing_id integer NOT NULL DEFAULT nextval('testing_thing_thing_id_seq'),
   thing_num smallint NOT NULL PRIMARY KEY DEFAULT 0,
   thing_desc varchar(100) NOT NULL
);

旁注：请记住，将序列附加到列并不会阻止用户手动用随机数据填充它，这可能会导致主键出现真正令人讨厌的问题。如果您想克服它并且不一定需要序列，请考虑创建一个标识列，例如

CREATE TABLE testing_thing(
   thing_id integer NOT NULL GENERATED ALWAYS AS IDENTITY,
   thing_num smallint NOT NULL PRIMARY KEY DEFAULT 0,
   thing_desc varchar(100) NOT NULL
);

演示：

db<>fiddle

Answer 2

CREATE TABLE testing_thing(
   thing_id integer NOT NULL ,
   thing_num smallint NOT NULL PRIMARY KEY DEFAULT 0,
   thing_desc varchar(100) NOT NULL
);

CREATE SEQUENCE IF NOT EXISTS testing_thing_thing_id_seq 
    INCREMENT 1
    START 1
    MINVALUE 1
    MAXVALUE 100
    CACHE 1
    OWNED BY testing_thing.thing_id;

ALTER TABLE testing_thing
  ALTER COLUMN thing_id SET DEFAULT nextval('testing_thing_thing_id_seq'::regclass);