Mysql Day 3 修改数据表

添加单列

mysql> ALTER TABLE users1 ADD age TINYINT UNSIGNED NOT NULL DEFAULT 10; //在users1中添加age列
Query OK, 0 rows affected (2.61 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> SHOW COLUMNS FROM users1;
+----------+----------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+----------------------+------+-----+---------+----------------+
| id | smallint(5) unsigned | NO | PRI | NULL | auto_increment |
| username | varchar(10) | NO | | NULL | |
| pid | smallint(5) unsigned | YES | MUL | NULL | |
| age | tinyint(3) unsigned | NO | | 10 | | //增加的列age
+----------+----------------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)

mysql> ALTER TABLE users1 ADD password VARCHAR(32) NOT NULL AFTER username; //在usersname后添加列password
Query OK, 0 rows affected (3.27 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> SHOW COLUMNS FROM users1;
+----------+----------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+----------------------+------+-----+---------+----------------+
| id | smallint(5) unsigned | NO | PRI | NULL | auto_increment |
| username | varchar(10) | NO | | NULL | |
| password | varchar(32) | NO | | NULL | |
| pid | smallint(5) unsigned | YES | MUL | NULL | |
| age | tinyint(3) unsigned | NO | | 10 | |
+----------+----------------------+------+-----+---------+----------------+
5 rows in set (0.00 sec)

mysql> ALTER TABLE users1 ADD turename VARCHAR(20) NOT NULL FIRST; //将列turename放在表的首位
Query OK, 0 rows affected (3.22 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> SHOW COLUMNS FROM users1;
+----------+----------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+----------------------+------+-----+---------+----------------+
| turename | varchar(20) | NO | | NULL | |
| id | smallint(5) unsigned | NO | PRI | NULL | auto_increment |
| username | varchar(10) | NO | | NULL | |
| password | varchar(32) | NO | | NULL | |
| pid | smallint(5) unsigned | YES | MUL | NULL | |
| age | tinyint(3) unsigned | NO | | 10 | |
+----------+----------------------+------+-----+---------+----------------+
6 rows in set (0.00 sec)

删除列

mysql> ALTER TABLE users1 DROP turename;
Query OK, 0 rows affected (0.91 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> SHOW COLUMNS FROM users1;
+----------+----------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+----------------------+------+-----+---------+----------------+
| id | smallint(5) unsigned | NO | PRI | NULL | auto_increment |
| username | varchar(10) | NO | | NULL | |
| password | varchar(32) | NO | | NULL | |
| pid | smallint(5) unsigned | YES | MUL | NULL | |
| age | tinyint(3) unsigned | NO | | 10 | |
+----------+----------------------+------+-----+---------+----------------+
5 rows in set (0.00 sec)

mysql> ALTER TABLE users1 DROP password,DROP age; //可以同时删除多个列，中间用逗号隔开
Query OK, 0 rows affected (1.25 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> CREATE TABLE users2(
-> username VARCHAR(10) NOT NULL,
-> pid SMALLINT UNSIGNED
-> );
Query OK, 0 rows affected (3.00 sec)

mysql> SHOW CREATE TABLE users2; //查看users2中包含的列
+--------+-------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+--------+-------------------------------------------------------------------------------------------------------------------------------------------+
| users2 | CREATE TABLE `users2` (
`username` varchar(10) NOT NULL,
`pid` smallint(5) unsigned DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+--------+-------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.05 sec)

mysql> ALTER TABLE users2 ADD id SMALLINT UNSIGNED; //添加列id
Query OK, 0 rows affected (2.55 sec)
Records: 0 Duplicates: 0 Warnings: 0

添加主键约束

mysql> ALTER TABLE users2 ADD CONSTRAINT PK_users2_id PRIMARY KEY(id); //将id设置为主键
Query OK, 0 rows affected (2.87 sec)
Records: 0 Duplicates: 0 Warnings: 0

添加唯一约束

mysql> ALTER TABLE users2 ADD UNIQUE(username); //将username设置为唯一约束
Query OK, 0 rows affected (2.55 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> SHOW CREATE TABLE users2;
+--------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+--------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| users2 | CREATE TABLE `users2` (
`username` varchar(10) NOT NULL,
`pid` smallint(5) unsigned DEFAULT NULL,
`id` smallint(5) unsigned NOT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `username` (`username`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+--------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

添加外键约束

mysql> ALTER TABLE users2 ADD FOREIGN KEY (pid) REFERENCES provinces(id); //将pid设置为外键约束
Query OK, 0 rows affected (1.03 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> SHOW CREATE TABLE users2;
+--------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+--------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| users2 | CREATE TABLE `users2` (
`username` varchar(10) NOT NULL,
`pid` smallint(5) unsigned DEFAULT NULL,
`id` smallint(5) unsigned NOT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `username` (`username`),
KEY `pid` (`pid`),
CONSTRAINT `users2_ibfk_1` FOREIGN KEY (`pid`) REFERENCES `provinces` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+--------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> ALTER TABLE users2 ADD age TINYINT UNSIGNED NOT NULL; //添加列age
Query OK, 0 rows affected (2.55 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> SHOW COLUMNS FROM users2;
+----------+----------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+----------------------+------+-----+---------+-------+
| username | varchar(10) | NO | UNI | NULL | |
| pid | smallint(5) unsigned | YES | MUL | NULL | |
| id | smallint(5) unsigned | NO | PRI | NULL | |
| age | tinyint(3) unsigned | NO | | NULL | |
+----------+----------------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

添加/删除默认约束

mysql> ALTER TABLE users2 ALTER age SET DEFAULT 15; //添加age的默认约束为15
Query OK, 0 rows affected (0.09 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> SHOW COLUMNS FROM users2;
+----------+----------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+----------------------+------+-----+---------+-------+
| username | varchar(10) | NO | UNI | NULL | |
| pid | smallint(5) unsigned | YES | MUL | NULL | |
| id | smallint(5) unsigned | NO | PRI | NULL | |
| age | tinyint(3) unsigned | NO | | 15 | |
+----------+----------------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

mysql> ALTER TABLE users2 ALTER age DROP DEFAULT; //删除age的默认约束
Query OK, 0 rows affected (2.47 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> SHOW COLUMNS FROM users2;
+----------+----------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+----------------------+------+-----+---------+-------+
| username | varchar(10) | NO | UNI | NULL | |
| pid | smallint(5) unsigned | YES | MUL | NULL | |
| id | smallint(5) unsigned | NO | PRI | NULL | |
| age | tinyint(3) unsigned | NO | | NULL | |
+----------+----------------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

删除主键约束

mysql> ALTER TABLE users2 DROP PRIMARY KEY;
Query OK, 0 rows affected (0.69 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> SHOW COLUMNS FROM users2;
+----------+----------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+----------------------+------+-----+---------+-------+
| username | varchar(10) | NO | PRI | NULL | |
| pid | smallint(5) unsigned | YES | MUL | NULL | |
| id | smallint(5) unsigned | NO | | NULL | | //id不再是主键
| age | tinyint(3) unsigned | NO | | NULL | |
+----------+----------------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

mysql> SHOW INDEXES FROM users2\G; //查看users2的索引，可以发现有两个索引
*************************** 1. row ***************************
Table: users2
Non_unique: 0
Key_name: username
Seq_in_index: 1
Column_name: username
Collation: A
Cardinality: 0
Sub_part: NULL
Packed: NULL
Null:
Index_type: BTREE
Comment:
Index_comment:
Visible: YES
Expression: NULL
*************************** 2. row ***************************
Table: users2
Non_unique: 1
Key_name: pid
Seq_in_index: 1
Column_name: pid
Collation: A
Cardinality: 0
Sub_part: NULL
Packed: NULL
Null: YES
Index_type: BTREE
Comment:
Index_comment:
Visible: YES
Expression: NULL
2 rows in set (0.00 sec)

ERROR:
No query specified

删除唯一约束

mysql> ALTER TABLE users2 DROP INDEX username;
Query OK, 0 rows affected (1.29 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> SHOW INDEXES FROM users2\G; //再次查看索引发现只剩下一个索引
*************************** 1. row ***************************
Table: users2
Non_unique: 1
Key_name: pid
Seq_in_index: 1
Column_name: pid
Collation: A
Cardinality: 0
Sub_part: NULL
Packed: NULL
Null: YES
Index_type: BTREE
Comment:
Index_comment:
Visible: YES
Expression: NULL
1 row in set (0.00 sec)

ERROR:
No query specified

删除外键约束

mysql> SHOW CREATE TABLE users2; //首先，查看外键的名称
+--------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+--------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| users2 | CREATE TABLE `users2` (
`username` varchar(10) NOT NULL,
`pid` smallint(5) unsigned DEFAULT NULL,
`id` smallint(5) unsigned NOT NULL,
`age` tinyint(3) unsigned NOT NULL,
KEY `pid` (`pid`),
CONSTRAINT `users2_ibfk_1` FOREIGN KEY (`pid`) REFERENCES `provinces` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+--------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> ALTER TABLE users2 DROP FOREIGN KEY users2_ibfk_1; //删除外键约束
Query OK, 0 rows affected (0.76 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> SHOW CREATE TABLE users2;
+--------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+--------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| users2 | CREATE TABLE `users2` (
`username` varchar(10) NOT NULL,
`pid` smallint(5) unsigned DEFAULT NULL,
`id` smallint(5) unsigned NOT NULL,
`age` tinyint(3) unsigned NOT NULL,
KEY `pid` (`pid`) //发现表users2中已经没有了外键约束，但还有一个键pid
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+--------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> ALTER TABLE users2 DROP INDEX pid; //删除索引pid
Query OK, 0 rows affected (0.58 sec)
Records: 0 Duplicates: 0 Warnings: 0

修改列定义

mysql> ALTER TABLE users2 MODIFY id SMALLINT UNSIGNED NOT NULL FIRST; //将字段id放在首位
Query OK, 0 rows affected (0.54 sec)
Records: 0 Duplicates: 0 Warnings: 0

mysql> ALTER TABLE users2 MODIFY id TINYINT UNSIGNED NOT NULL FIRST; //将id的类型改为tinyint并置于首位
Query OK, 0 rows affected (3.10 sec)
Records: 0 Duplicates: 0 Warnings: 0

修改列名称（change也可用来修改列定义）

mysql> ALTER TABLE users2 CHANGE pid p_id TINYINT UNSIGNED NOT NULL; //将pid改为p_id
Query OK, 0 rows affected (3.23 sec)
Records: 0 Duplicates: 0 Warnings: 0

数据表更名（两种方法）

mysql> ALTER TABLE users2 RENAME users3; //将users2改为users3（方法1）
Query OK, 0 rows affected (1.25 sec)

mysql> RENAME TABLE users3 TO users2; //将users3改为users2（方法2）
Query OK, 0 rows affected (0.65 sec)

Mysql Day 3 修改数据表

添加单列

删除列

添加主键约束

添加唯一约束

添加外键约束

添加/删除默认约束

删除主键约束

删除唯一约束

删除外键约束

修改列定义

修改列名称（change也可用来修改列定义）

数据表更名（两种方法）

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