如何创建一个创建MySQL数据库中的datetime类型

环境系统平台：microsoft windows (64-bit) 10版本：4.5

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)。

一、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

二、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)

三、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);

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