怎么创建一个创建MySQL数据库中的datetime类型

今天小编给大家分享一下怎么创建一个创建MySQL数据库中的datetime类型的相关知识点，内容详细，逻辑清晰，相信大部分人都还太了解这方面的知识，所以分享这篇文章给大家参考一下，希望大家阅读完这篇文章后有所收获，下面我们一起来了解一下吧。

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 ashighgo-# text not nullhighgo-# check (highgo(#     length(value) = 32highgo(# );CREATE DOMAINhighgo=# 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 TABLEhighgo=# 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 TABLEhighgo=# \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: heaphighgo=# insert into t_time values (1,now()),(2,now());INSERT 0 2highgo=# 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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