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MySQL中兩種快速創建空表的方式的區別

來源:互聯網  2008-06-12 07:23:59  評論

在MySQL中有兩種方法

1、create table t_name select ...

2、create table t_name like ...

第一種會取消掉原來表的有些定義,且引擎是系統默認引擎。

手冊上是這麽講的:Some conversion of data types might occur. For example, the AUTO_INCREMENT attribute is not preserved, and VARCHAR columns can become CHAR columns.

第二種就完全複制原表。

先建立測試表:

mysql> create database dbtest;

Query OK, 1 row affected (0.03 sec)

mysql> use dbtest;

Database changed

mysql> create table t_old

-> (

-> id serial,

-> content varchar(8000) not null,

-> `desc` varchar(100) not null)

-> engine innodb;

Query OK, 0 rows affected (0.04 sec)

mysql> show create table t_old;

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

| Table | Create Table |

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

| t_old | CREATE TABLE `t_old` (

`id` bigint(20) unsigned NOT NULL auto_increment,

`content` varchar(8000) NOT NULL,

`desc` varchar(100) NOT NULL,

UNIQUE KEY `id` (`id`)

) ENGINE=InnoDB DEFAULT CHARSET=latin1 |

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

1 row in set (0.00 sec)

第一種方式:

mysql> create table t_select select * from t_old where 1 = 0;

Query OK, 0 rows affected (0.04 sec)

Records: 0 Duplicates: 0 Warnings: 0

mysql> show create table t_select;

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

| Table | Create Table +----------+---------------------------------------------+

| t_select | CREATE TABLE `t_select` (

`id` bigint(20) unsigned NOT NULL default '0',

`content` varchar(8000) NOT NULL,

`desc` varchar(100) NOT NULL

) ENGINE=MyISAM DEFAULT CHARSET=latin1 |

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

1 row in set (0.00 sec)

第二種方式:

mysql> create table t_like like t_old;

Query OK, 0 rows affected (0.02 sec)

mysql> show create table t_like;

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

| Table | Create Table |

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

| t_like | CREATE TABLE `t_like` (

`id` bigint(20) unsigned NOT NULL auto_increment,

`content` varchar(8000) NOT NULL,

`desc` varchar(100) NOT NULL,

UNIQUE KEY `id` (`id`)

) ENGINE=InnoDB DEFAULT CHARSET=latin1 |

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

1 row in set (0.00 sec)

mysql>

在MySQL中有兩種方法 1、create table t_name select ... 2、create table t_name like ... 第一種會取消掉原來表的有些定義,且引擎是系統默認引擎。 手冊上是這麽講的:Some conversion of data types might occur. For example, the AUTO_INCREMENT attribute is not preserved, and VARCHAR columns can become CHAR columns. 第二種就完全複制原表。 先建立測試表: mysql> create database dbtest; Query OK, 1 row affected (0.03 sec) mysql> use dbtest; Database changed mysql> create table t_old -> ( -> id serial, -> content varchar(8000) not null, -> `desc` varchar(100) not null) -> engine innodb; Query OK, 0 rows affected (0.04 sec) mysql> show create table t_old; +-------+-------------------------------------------------+ | Table | Create Table | +-------+------------------------------------------------+ | t_old | CREATE TABLE `t_old` ( `id` bigint(20) unsigned NOT NULL auto_increment, `content` varchar(8000) NOT NULL, `desc` varchar(100) NOT NULL, UNIQUE KEY `id` (`id`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 | +-------+----------------------------------------------------+ 1 row in set (0.00 sec) 第一種方式: mysql> create table t_select select * from t_old where 1 = 0; Query OK, 0 rows affected (0.04 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> show create table t_select; +----------+--------------------------------------------+ | Table | Create Table +----------+---------------------------------------------+ | t_select | CREATE TABLE `t_select` ( `id` bigint(20) unsigned NOT NULL default '0', `content` varchar(8000) NOT NULL, `desc` varchar(100) NOT NULL ) ENGINE=MyISAM DEFAULT CHARSET=latin1 | +----------+-------------------------------------------+ 1 row in set (0.00 sec) 第二種方式: mysql> create table t_like like t_old; Query OK, 0 rows affected (0.02 sec) mysql> show create table t_like; +--------+-------------------------------------------------+ | Table | Create Table | +--------+-------------------------------------------------+ | t_like | CREATE TABLE `t_like` ( `id` bigint(20) unsigned NOT NULL auto_increment, `content` varchar(8000) NOT NULL, `desc` varchar(100) NOT NULL, UNIQUE KEY `id` (`id`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 | +--------+-------------------------------------------------+ 1 row in set (0.00 sec) mysql>
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