创建一个MySQL数据库中的datetime类型

瀚高数据库
目录
环境
文档用途
详细信息

环境
系统平台：Microsoft Windows (64-bit) 10
版本：4.5
文档用途
介绍瀚高数据库中创建一个datetime类型的方法以及create domain 和create type的用法和区别。

详细信息
瀚高数据库中支持使用以下语句创建用户定义的数据类型：

CREATE DOMAIN：它创建了一个用户定义的数据类型，可以有可选的约束，基于其他基本类型，实质是定义一个域。

CREATE TYPE：它通常用于使用存储过程创建复合类型(两种或多种数据类型混合的数据类型)。

domain用法及示例
假如有以下表结构：

create table test_domain (id varchar,md5 text not null check(length(md5)=32));

其中md5列的类型及约束，可以定义一个domain来抽象，如下：

highgo=# create domain md5 as

highgo-# text not null

highgo-# check (

highgo(#     length(value) = 32

highgo(# );

CREATE DOMAIN

highgo=# 



highgo=# \dD md5

                                  List of domains

 Schema | Name | Type | Collation | Nullable | Default |           Check            

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

 public | md5  | text |           | not null |         | CHECK (length(VALUE) = 32)

(1 row)



highgo=# create table test_domain (id varchar,md5 md5);

CREATE TABLE

highgo=# insert into test_domain values('1','2');

ERROR:  value for domain md5 violates check constraint "md5_check"

highgo=# insert into test_domain values('2','76a2173be6393254e72ffa4d6df1030a');

INSERT 0 1

创建MySQL中datetime类型

highgo=# create domain datetime as timestamp without time zone;

highgo=# create table t_time (id int,create_time datetime);

CREATE TABLE

highgo=# \d+ t_time

                                     Table "public.t_time"

   Column    |   Type   | Collation | Nullable | Default | Storage | Stats target | Description 

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

 id          | integer  |           |          |         | plain   |              | 

 create_time | datetime |           |          |         | plain   |              | 

Access method: heap

highgo=# insert into t_time values (1,now()),(2,now());

INSERT 0 2

highgo=# 

highgo=# select * from t_time;

 id |        create_time         

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

  1 | 2021-08-03 19:28:11.207324

  2 | 2021-08-03 19:28:11.207324

(2 rows)

create type用法及示例

CREATE TYPE name AS

    ( [ attribute_name data_type [ COLLATE collation ] [, ... ] ] )



CREATE TYPE name AS ENUM

    ( [ 'label' [, ... ] ] )



CREATE TYPE name AS RANGE (

    SUBTYPE = subtype

    [ , SUBTYPE_OPCLASS = subtype_operator_class ]

    [ , COLLATION = collation ]

    [ , CANONICAL = canonical_function ]

    [ , SUBTYPE_DIFF = subtype_diff_function ]

)



CREATE TYPE name (

    INPUT = input_function,

    OUTPUT = output_function

    [ , RECEIVE = receive_function ]

    [ , SEND = send_function ]

    [ , TYPMOD_IN = type_modifier_input_function ]

    [ , TYPMOD_OUT = type_modifier_output_function ]

    [ , ANALYZE = analyze_function ]

    [ , INTERNALLENGTH = { internallength | VARIABLE } ]

    [ , PASSEDBYVALUE ]

    [ , ALIGNMENT = alignment ]

    [ , STORAGE = storage ]

    [ , LIKE = like_type ]

    [ , CATEGORY = category ]

    [ , PREFERRED = preferred ]

    [ , DEFAULT = default ]

    [ , ELEMENT = element ]

    [ , DELIMITER = delimiter ]

    [ , COLLATABLE = collatable ]

)



CREATE TYPE name

创建示例：

CREATE TYPE compfoo AS (f1 int, f2 text);



CREATE FUNCTION getfoo() RETURNS SETOF compfoo AS $$

    SELECT fooid, fooname FROM foo

$$ LANGUAGE SQL;

CREATE TYPE bug_status AS ENUM ('new', 'open', 'closed');



CREATE TABLE bug (

    id serial,

    description text,

    status bug_status

);

CREATE TYPE float8_range AS RANGE (subtype = float8, subtype_diff = float8mi);