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器量大者,福泽必厚

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分类: LINUX

2014-01-07 17:08:18

mysql> create table test1(id int unsigned not null,first_name varchar(30) not null,last_name varchar(30) not null,joined date not null,primary key(id),index(id));
Query OK, 0 rows affected (0.02 sec)

mysql> show create table test1;
+-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                                                                                                                                                                     |
+-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| test1 | CREATE TABLE `test1` (
  `id` int(10) unsigned NOT NULL,
  `first_name` varchar(30) COLLATE utf8_unicode_ci NOT NULL,
  `last_name` varchar(30) COLLATE utf8_unicode_ci NOT NULL,
  `joined` date NOT NULL,
  PRIMARY KEY (`id`),
  KEY `id` (`id`)    ##注意蓝色和绿色的区别
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci |
+-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> alter table test1 drop index id;
Query OK, 0 rows affected (0.00 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> show create table test1;
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                                                                                                                                                  |
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| test1 | CREATE TABLE `test1` (
  `id` int(10) unsigned NOT NULL,
  `first_name` varchar(30) COLLATE utf8_unicode_ci NOT NULL,
  `last_name` varchar(30) COLLATE utf8_unicode_ci NOT NULL,
  `joined` date NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci |
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> show indexes from test1;
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| test1 |          0 | PRIMARY  |            1 | id          | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
1 row in set (0.00 sec)

mysql> alter table test1 add index id(id);
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> show create table test1;
+-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                                                                                                                                                                     |
+-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| test1 | CREATE TABLE `test1` (
  `id` int(10) unsigned NOT NULL,
  `first_name` varchar(30) COLLATE utf8_unicode_ci NOT NULL,
  `last_name` varchar(30) COLLATE utf8_unicode_ci NOT NULL,
  `joined` date NOT NULL,
  PRIMARY KEY (`id`),
  KEY `id` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci |
+-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)


mysql> create table test2(id int unsigned not null,first_name varchar(30) not null,last_name varchar(30) not null,joined date not null,primary key(id),key(id));
Query OK, 0 rows affected (0.01 sec)
##换成key也一样!


mysql> show create table test2;
+-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                                                                                                                                                                     |
+-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| test2 | CREATE TABLE `test2` (
  `id` int(10) unsigned NOT NULL,
  `first_name` varchar(30) COLLATE utf8_unicode_ci NOT NULL,
  `last_name` varchar(30) COLLATE utf8_unicode_ci NOT NULL,
  `joined` date NOT NULL,
  PRIMARY KEY (`id`),
  KEY `id` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci |
+-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

个人理解,index和key没区别,一样的东西

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