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MySQL中两种快速创建空表的方式的区别
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在MySQL中有两种方法
1、create table t_name select ...
2、create table t_name like ...
第一种会取消掉原来表的有些定义，且引擎是系统默认引擎。
手册上是这么讲的：Some conversion of data types might occur. For example, the AUTO_INCREMENT attribute is not preserved, and VARCHAR columns can become CHAR columns.
第二种就完全复制原表。
先建立测试表:
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)
第一种方式：
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)
第二种方式：
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>
1、create table t_name select ...
2、create table t_name like ...
第一种会取消掉原来表的有些定义，且引擎是系统默认引擎。
手册上是这么讲的：Some conversion of data types might occur. For example, the AUTO_INCREMENT attribute is not preserved, and VARCHAR columns can become CHAR columns.
第二种就完全复制原表。
先建立测试表:
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)
第一种方式：
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)
第二种方式：
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>