|
今天有人问我用什么方法可以创建空表？
在MYSQL中有两种方法。
1、create table select ...
2、create table like ...
第一种很多人都知道，第二种却很少人用。
第一种有两个缺点
1、第一种会取消掉原来表的有些定义。
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.
不过我测试过，只会取消自增属性！
2、引擎是系统默认引擎。
第二种就不会。
我们来看看例子：
mysql> create table t_old (id serial, content varchar(8000) not null,`desc` varchar(100) not null) engine innodb;
Query OK, 0 rows affected (0.01 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=utf8 |
+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
mysql> create table t_select select * from t_old where 1 = 0;
Query OK, 0 rows affected (0.01 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=utf8 |
+----------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
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=utf8 |
+--------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
mysql>
|
