07.数据表的修改

用上文的user1表，查看表结构：

mysql> DESC user1;
+----------+----------------------+------+-----+---------+----------------+
| Field    | Type                 | Null | Key | Default | Extra          |
+----------+----------------------+------+-----+---------+----------------+
| id       | smallint(5) unsigned | NO   | PRI | NULL    | auto_increment |
| username | varchar(20)          | NO   |     | NULL    |                |
| p_id     | smallint(5) unsigned | YES  | MUL | NULL    |                |
+----------+----------------------+------+-----+---------+----------------+
3 rows in set (0.00 sec)

添加一个默认值为10的非空字段

mysql> ALTER TABLE user1 ADD age SMALLINT UNSIGNED NOT NULL DEFAULT 10;
Query OK, 0 rows affected (0.06 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> DESC user1;
+----------+----------------------+------+-----+---------+----------------+
| Field    | Type                 | Null | Key | Default | Extra          |
+----------+----------------------+------+-----+---------+----------------+
| id       | smallint(5) unsigned | NO   | PRI | NULL    | auto_increment |
| username | varchar(20)          | NO   |     | NULL    |                |
| p_id     | smallint(5) unsigned | YES  | MUL | NULL    |                |
| age      | smallint(5) unsigned | NO   |     | 10      |                |
+----------+----------------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)

在某列后添加字段：AFTER(FIRST添加到最前面)

mysql> ALTER TABLE user1 ADD password VARCHAR(32) NOT NULL AFTER username;
Query OK, 0 rows affected (0.09 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> DESC user1;
+----------+----------------------+------+-----+---------+----------------+
| Field    | Type                 | Null | Key | Default | Extra          |
+----------+----------------------+------+-----+---------+----------------+
| id       | smallint(5) unsigned | NO   | PRI | NULL    | auto_increment |
| username | varchar(20)          | NO   |     | NULL    |                |
| password | varchar(32)          | NO   |     | NULL    |                |
| p_id     | smallint(5) unsigned | YES  | MUL | NULL    |                |
| age      | smallint(5) unsigned | NO   |     | 10      |                |
+----------+----------------------+------+-----+---------+----------------+
5 rows in set (0.00 sec)

添加多列：

mysql> ALTER TABLE user1 ADD (aaa VARCHAR(32), bbb VARCHAR(32),ccc VARCHAR(32));
Query OK, 0 rows affected (0.09 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> DESC user1;
+----------+----------------------+------+-----+---------+----------------+
| Field    | Type                 | Null | Key | Default | Extra          |
+----------+----------------------+------+-----+---------+----------------+
| sax      | varchar(32)          | NO   |     | NULL    |                |
| id       | smallint(5) unsigned | NO   | PRI | NULL    | auto_increment |
| username | varchar(20)          | NO   |     | NULL    |                |
| password | varchar(32)          | NO   |     | NULL    |                |
| p_id     | smallint(5) unsigned | YES  | MUL | NULL    |                |
| age      | smallint(5) unsigned | NO   |     | 10      |                |
| aaa      | varchar(32)          | YES  |     | NULL    |                |
| bbb      | varchar(32)          | YES  |     | NULL    |                |
| ccc      | varchar(32)          | YES  |     | NULL    |                |
+----------+----------------------+------+-----+---------+----------------+
9 rows in set (0.00 sec)

删除列aaa:

mysql> ALTER TABLE user1 DROP aaa;
Query OK, 0 rows affected (0.45 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> DESC user1;
+----------+----------------------+------+-----+---------+----------------+
| Field    | Type                 | Null | Key | Default | Extra          |
+----------+----------------------+------+-----+---------+----------------+
| sax      | varchar(32)          | NO   |     | NULL    |                |
| id       | smallint(5) unsigned | NO   | PRI | NULL    | auto_increment |
| username | varchar(20)          | NO   |     | NULL    |                |
| password | varchar(32)          | NO   |     | NULL    |                |
| p_id     | smallint(5) unsigned | YES  | MUL | NULL    |                |
| age      | smallint(5) unsigned | NO   |     | 10      |                |
| bbb      | varchar(32)          | YES  |     | NULL    |                |
| ccc      | varchar(32)          | YES  |     | NULL    |                |
+----------+----------------------+------+-----+---------+----------------+
8 rows in set (0.00 sec)

同时删除两列：bbb，ccc

mysql> ALTER TABLE user1 DROP bbb,DROP ccc;
Query OK, 0 rows affected (0.08 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> DESC user1;
+----------+----------------------+------+-----+---------+----------------+
| Field    | Type                 | Null | Key | Default | Extra          |
+----------+----------------------+------+-----+---------+----------------+
| sax      | varchar(32)          | NO   |     | NULL    |                |
| id       | smallint(5) unsigned | NO   | PRI | NULL    | auto_increment |
| username | varchar(20)          | NO   |     | NULL    |                |
| password | varchar(32)          | NO   |     | NULL    |                |
| p_id     | smallint(5) unsigned | YES  | MUL | NULL    |                |
| age      | smallint(5) unsigned | NO   |     | 10      |                |
+----------+----------------------+------+-----+---------+----------------+
6 rows in set (0.00 sec)

删除主键约束:(必须是没有自增长的主键，自增长要依附于主键删不了，key_test符合)

mysql> ALTER TABLE user1 DROP PRIMARY KEY;
ERROR 1075 (42000): Incorrect table definition; there can be only one auto column and it must be defined as a key

mysql> DESC key_test;
+----------+----------------------+------+-----+---------+-------+
| Field    | Type                 | Null | Key | Default | Extra |
+----------+----------------------+------+-----+---------+-------+
| id       | smallint(5) unsigned | NO   | PRI | NULL    |       |
| username | varchar(20)          | YES  |     | NULL    |       |
+----------+----------------------+------+-----+---------+-------+
2 rows in set (0.00 sec)
mysql> ALTER TABLE key_test DROP PRIMARY KEY;
Query OK, 2 rows affected (0.05 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql> DESC key_test;
+----------+----------------------+------+-----+---------+-------+
| Field    | Type                 | Null | Key | Default | Extra |
+----------+----------------------+------+-----+---------+-------+
| id       | smallint(5) unsigned | NO   |     | NULL    |       |
| username | varchar(20)          | YES  |     | NULL    |       |
+----------+----------------------+------+-----+---------+-------+
2 rows in set (0.00 sec)

删除唯一约束

mysql> SHOW INDEXES FROM unique_test;
+-------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table       | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| unique_test |          0 | PRIMARY  |            1 | id          | A         |           2 |     NULL | NULL   |      | BTREE      |         |               |
| unique_test |          0 | username |            1 | username    | A         |           2 |     NULL | NULL   | YES  | BTREE      |         |               |
+-------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
mysql> ALTER TABLE unique_test DROP INDEX username;
Query OK, 0 rows affected (0.39 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> SHOW INDEXES FROM unique_test;
+-------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table       | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| unique_test |          0 | PRIMARY  |            1 | id          | A         |           2 |     NULL | NULL   |      | BTREE      |         |               |
+-------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
1 row in set (0.00 sec)

删除外键约束：注意外键约束名：user1_ibfk_1

mysql> SHOW CREATE TABLE user1;
+-------+---------------------------------------------------------------------------------------
------------------------------------------------------------------------------------------------
-------------------------------------+
| Table | Create Table

                                     |
+-------+---------------------------------------------------------------------------------------
------------------------------------------------------------------------------------------------
-------------------------------------+
| user1 | CREATE TABLE `user1` (
  `sax` varchar(32) NOT NULL,
  `id` smallint(5) unsigned NOT NULL AUTO_INCREMENT,
  `username` varchar(20) NOT NULL,
  `password` varchar(32) NOT NULL,
  `p_id` smallint(5) unsigned DEFAULT NULL,
  `age` smallint(5) unsigned NOT NULL DEFAULT '10',
  PRIMARY KEY (`id`),
  KEY `p_id` (`p_id`),
  CONSTRAINT `user1_ibfk_1` FOREIGN KEY (`p_id`) REFERENCES `province` (`id`) ON DELETE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8 |
+-------+---------------------------------------------------------------------------------------
------------------------------------------------------------------------------------------------
-------------------------------------+
1 row in set (0.41 sec)
mysql> ALTER TABLE user1 DROP FOREIGN KEY user1_ibfk_1;
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> SHOW CREATE TABLE user1;
+-------+-------------------------------------------------------------
----------------------------------------------------------------------
| Table | Create Table

+-------+-------------------------------------------------------------
----------------------------------------------------------------------
| user1 | CREATE TABLE `user1` (
  `sax` varchar(32) NOT NULL,
  `id` smallint(5) unsigned NOT NULL AUTO_INCREMENT,
  `username` varchar(20) NOT NULL,
  `password` varchar(32) NOT NULL,
  `p_id` smallint(5) unsigned DEFAULT NULL,
  `age` smallint(5) unsigned NOT NULL DEFAULT '10',
  PRIMARY KEY (`id`),
  KEY `p_id` (`p_id`)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8 |
+-------+-------------------------------------------------------------
----------------------------------------------------------------------
1 row in set (0.00 sec)

外键去除后，索引p_id就没有用了，也可以去除：

mysql> ALTER TABLE user1 DROP INDEX p_id;
Query OK, 0 rows affected (0.39 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> SHOW CREATE TABLE user1;
+-------+--------------------------------------------------------
-----------------------------------------------------------------
| Table | Create Table

+-------+--------------------------------------------------------
-----------------------------------------------------------------
| user1 | CREATE TABLE `user1` (
  `sax` varchar(32) NOT NULL,
  `id` smallint(5) unsigned NOT NULL AUTO_INCREMENT,
  `username` varchar(20) NOT NULL,
  `password` varchar(32) NOT NULL,
  `p_id` smallint(5) unsigned DEFAULT NULL,
  `age` smallint(5) unsigned NOT NULL DEFAULT '10',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8 |
+-------+--------------------------------------------------------
-----------------------------------------------------------------
1 row in set (0.00 sec)

修改列的位置：想把user1中的id调到最上面

mysql> DESC user1;
+----------+----------------------+------+-----+---------+----------------+
| Field    | Type                 | Null | Key | Default | Extra          |
+----------+----------------------+------+-----+---------+----------------+
| sax      | varchar(32)          | NO   |     | NULL    |                |
| id       | smallint(5) unsigned | NO   | PRI | NULL    | auto_increment |
| username | varchar(20)          | NO   |     | NULL    |                |
| password | varchar(32)          | NO   |     | NULL    |                |
| p_id     | smallint(5) unsigned | YES  |     | NULL    |                |
| age      | smallint(5) unsigned | NO   |     | 10      |                |
+----------+----------------------+------+-----+---------+----------------+
6 rows in set (0.00 sec)

mysql> ALTER TABLE user1 MODIFY id SMALLINT UNSIGNED NOT NULL FIRST;
Query OK, 2 rows affected (0.44 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql> DESC user1;
+----------+----------------------+------+-----+---------+-------+
| Field    | Type                 | Null | Key | Default | Extra |
+----------+----------------------+------+-----+---------+-------+
| id       | smallint(5) unsigned | NO   | PRI | NULL    |       |
| sax      | varchar(32)          | NO   |     | NULL    |       |
| username | varchar(20)          | NO   |     | NULL    |       |
| password | varchar(32)          | NO   |     | NULL    |       |
| p_id     | smallint(5) unsigned | YES  |     | NULL    |       |
| age      | smallint(5) unsigned | NO   |     | 10      |       |
+----------+----------------------+------+-----+---------+-------+
6 rows in set (0.01 sec)

修改列信息：将sax改为gender更好一点，再把长度改短点

mysql> ALTER TABLE user1 CHANGE sax gender VARCHAR(4) NOT NULL;
Query OK, 2 rows affected (0.06 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql> DESC user1;
+----------+----------------------+------+-----+---------+-------+
| Field    | Type                 | Null | Key | Default | Extra |
+----------+----------------------+------+-----+---------+-------+
| id       | smallint(5) unsigned | NO   | PRI | NULL    |       |
| gender   | varchar(4)           | NO   |     | NULL    |       |
| username | varchar(20)          | NO   |     | NULL    |       |
| password | varchar(32)          | NO   |     | NULL    |       |
| p_id     | smallint(5) unsigned | YES  |     | NULL    |       |
| age      | smallint(5) unsigned | NO   |     | 10      |       |
+----------+----------------------+------+-----+---------+-------+
6 rows in set (0.01 sec)

表名user1不抢眼，改个名字吧

mysql> ALTER TABLE user1 RENAME 阿姆斯特朗回旋加速喷气式阿姆斯特朗炮;
Query OK, 0 rows affected (0.01 sec)

mysql> SHOW TABLES;
+--------------------------------------------------------+
| Tables_in_zoom                                         |
+--------------------------------------------------------+
| 阿姆斯特朗回旋加速喷气式阿姆斯特朗炮                   |
| default_                                               |
| key_test                                               |
| little                                                 |
| null_test                                              |
| province                                               |
| unique_id                                              |
| unique_test                                            |
| users                                                  |
+--------------------------------------------------------+
9 rows in set (0.00 sec)

不行，太装X,用另一种方法改个低调的

mysql> RENAME TABLE 阿姆斯特朗回旋加速喷气式阿姆斯特朗炮 TO toly;
Query OK, 0 rows affected (0.01 sec)

mysql> SHOW TABLES;
+----------------+
| Tables_in_zoom |
+----------------+
| default_       |
| key_test       |
| little         |
| null_test      |
| province       |
| toly           |
| unique_id      |
| unique_test    |
| users          |
+----------------+
9 rows in set (0.00 sec)