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：
其中md5列的类型及约束，可以定义一个domain来抽象，如下：
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 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
( [ 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 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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