mysql三：表操作
一、存储引擎介绍
存储引擎即表类型，mysql根据不同的表类型会有不同的处理机制。
详见：点击查看
二、表的介绍
表相当于文件，表中的一条记录就相当于文件的一行内容，不同的是，表中的一条记录有对应的标题，称为表的字段。
id，name，qq，age称为字段，其余的，一行内容称为一条记录。
三、创建表
#语法：
create table 表名(
字段名1 类型[(宽度) 约束条件],
字段名2 类型[(宽度) 约束条件],
字段名3 类型[(宽度) 约束条件]
); #注意：
1. 在同一张表中，字段名是不能相同
2. 宽度和约束条件可选
3. 字段名和类型是必须的
mysql> create database db2 charset utf8;
Query OK, 1 row affected (0.01 sec) mysql> use db2
Database changed
mysql> create table t1(
-> id int,
-> name varchar(50),
-> sex enum('male', 'female'),
-> age int(3)
-> );
Query OK, 0 rows affected (0.01 sec) mysql> show tables;
+---------------+
| Tables_in_db2 |
+---------------+
| t1 |
+---------------+
1 row in set (0.00 sec) mysql> desc t1;
+-------+-----------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-----------------------+------+-----+---------+-------+
| id | int(11) | YES | | NULL | |
| name | varchar(50) | YES | | NULL | |
| sex | enum('male','female') | YES | | NULL | |
| age | int(3) | YES | | NULL | |
+-------+-----------------------+------+-----+---------+-------+
4 rows in set (0.01 sec) mysql> select id,name,sex,age from t1;
Empty set (0.00 sec) mysql> select * from t1;
Empty set (0.00 sec)
创表示例
mysql> insert into t1 values (1,'egon','male',18), (2,'alex','female',81);
Query OK, 2 rows affected (0.00 sec)
Records: 2 Duplicates: 0 Warnings: 0 mysql> select * from t1;
+------+------+--------+------+
| id | name | sex | age |
+------+------+--------+------+
| 1 | egon | male | 18 |
| 2 | alex | female | 81 |
+------+------+--------+------+
2 rows in set (0.00 sec) mysql> insert into t1(id) values
-> (3),
-> (4);
Query OK, 2 rows affected (0.01 sec)
Records: 2 Duplicates: 0 Warnings: 0 mysql> select * from t1;
+------+------+--------+------+
| id | name | sex | age |
+------+------+--------+------+
| 1 | egon | male | 18 |
| 2 | alex | female | 81 |
| 3 | NULL | NULL | NULL |
| 4 | NULL | NULL | NULL |
+------+------+--------+------+
4 rows in set (0.00 sec)
往表中插入数据
特别需要注意：字段匹配顺序和表中最后一个字段不能加逗号。
四、查看表结构
mysql> describe t1;
+-------+-----------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-----------------------+------+-----+---------+-------+
| id | int(11) | YES | | NULL | |
| name | varchar(50) | YES | | NULL | |
| sex | enum('male','female') | YES | | NULL | |
| age | int(3) | YES | | NULL | |
+-------+-----------------------+------+-----+---------+-------+
4 rows in set (0.00 sec) mysql> show create table t1\G; # 查看表结构详细结构，可以添加\G
类似的show create table mysql.user\G; 执行查看，可以解决在屏幕比较小时，“----”显示混乱的问题。
五、数据类型
详见：点击插看
六、表完整性约束
详见：点击查看
七、修改表结构
语法：
1. 修改表名
ALTER TABLE 表名
RENAME 新表名; 2. 增加字段
ALTER TABLE 表名
ADD 字段名 数据类型 [完整性约束条件…], # 添加多个字段
ADD 字段名 数据类型 [完整性约束条件…];
ALTER TABLE 表名
ADD 字段名 数据类型 [完整性约束条件…] FIRST; # 添加新字段到第一个
ALTER TABLE 表名
ADD 字段名 数据类型 [完整性约束条件…] AFTER 字段名; # 添加新字段到指定字段之后 3. 删除字段
ALTER TABLE 表名
DROP 字段名; 4. 修改字段————主要针对字段类型和字段名称
ALTER TABLE 表名
MODIFY 字段名 数据类型 [完整性约束条件…]; # 修改字段类型
ALTER TABLE 表名
CHANGE 旧字段名 新字段名 旧数据类型 [完整性约束条件…]; # 修改字段名称
ALTER TABLE 表名
CHANGE 旧字段名 新字段名 新数据类型 [完整性约束条件…];
示例：
mysql> use db2
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A Database changed
mysql> create table service;
ERROR 1113 (42000): A table must have at least 1 column
mysql> create table service(id int);
Query OK, 0 rows affected (0.02 sec) # 1、修改存储引擎
mysql> alter table service
-> engine=innodb;
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0 mysql> create table student10(id int);
Query OK, 0 rows affected (0.01 sec) # 2、添加字段
mysql> alter table student10
-> add name varchar(20) not null,
-> add age int(3) not null default 22;
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0 mysql> alter table student10
-> add stu_num varchar(10) not null after name; # after关键词，添加到name字段后
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0 mysql> alter table student10
-> add sex enum('male', 'female') default 'male' first; # first关键词，添加到最前面
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0 mysql> select * from student10;
Empty set (0.00 sec) mysql> describe student10; # 查看表结构
+---------+-----------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+-----------------------+------+-----+---------+-------+
| sex | enum('male','female') | YES | | male | |
| id | int(11) | YES | | NULL | |
| name | varchar(20) | NO | | NULL | |
| stu_num | varchar(10) | NO | | NULL | |
| age | int(3) | NO | | 22 | |
+---------+-----------------------+------+-----+---------+-------+
5 rows in set (0.00 sec) # 3、删除字段
mysql> alter table student10
-> drop sex;
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0 mysql> alter table service add mac varchar(20);
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0 mysql> alter table service drop mac;
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0 mysql> describe student10;
+---------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| id | int(11) | YES | | NULL | |
| name | varchar(20) | NO | | NULL | |
| stu_num | varchar(10) | NO | | NULL | |
| age | int(3) | NO | | 22 | |
+---------+-------------+------+-----+---------+-------+
4 rows in set (0.00 sec) # 4、修改字段类型modify
mysql> alter table student10
-> modify age int(3);
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0 mysql> alter table student10
-> modify id int(11) not null primary key auto_increment; # 修改为主键
Query OK, 0 rows affected (0.04 sec)
Records: 0 Duplicates: 0 Warnings: 0 mysql> select * from student10;
Empty set (0.01 sec) mysql> describe student10;
+---------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(20) | NO | | NULL | |
| stu_num | varchar(10) | NO | | NULL | |
| age | int(3) | YES | | NULL | |
+---------+-------------+------+-----+---------+----------------+
4 rows in set (0.00 sec) # 5、增加约束（针对已有的主键添加auto_increment）
mysql> alter table student10 modify id int(11) not null primary key auto_increment;
ERROR 1068 (42000): Multiple primary key defined mysql> alter table student10 modify id int(11) not null auto_increment;
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0 mysql> describe student10;
+---------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(20) | NO | | NULL | |
| stu_num | varchar(10) | NO | | NULL | |
| age | int(3) | YES | | NULL | |
+---------+-------------+------+-----+---------+----------------+
4 rows in set (0.00 sec) # 6、对已经存在的表添加复合主键
mysql> alter table service
-> add host_ip varchar(24),
-> add port int(4);
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0 mysql> describe service;
+---------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| id | int(11) | YES | | NULL | |
| host_ip | varchar(24) | YES | | NULL | |
| port | int(4) | YES | | NULL | |
+---------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec) mysql> alter table service
-> add primary key(host_ip, port); # 增加复合主键，经测试必须是这个字段存在
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0 mysql> describe service;
+---------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| id | int(11) | YES | | NULL | |
| host_ip | varchar(24) | NO | PRI | NULL | |
| port | int(4) | NO | PRI | NULL | |
+---------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec) # 7、删除主键
# a.删除自增约束
mysql> describe student10;
+---------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(20) | NO | | NULL | |
| stu_num | varchar(10) | NO | | NULL | |
| age | int(3) | YES | | NULL | |
+---------+-------------+------+-----+---------+----------------+
4 rows in set (0.00 sec) mysql> alter table student10
-> modify name varchar(10) not null primary key;
ERROR 1068 (42000): Multiple primary key defined
mysql> alter table student10
-> 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> alter table student10
-> modify id int(11) not null;
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0 mysql> describe student10;
+---------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| id | int(11) | NO | PRI | NULL | |
| name | varchar(20) | NO | | NULL | |
| stu_num | varchar(10) | NO | | NULL | |
| age | int(3) | YES | | NULL | |
+---------+-------------+------+-----+---------+-------+
4 rows in set (0.00 sec) # b.删除主键
mysql> alter table student10
-> drop primary key;
Query OK, 0 rows affected (0.03 sec)
Records: 0 Duplicates: 0 Warnings: 0 mysql> describe student10;
+---------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| id | int(11) | NO | | NULL | |
| name | varchar(20) | NO | | NULL | |
| stu_num | varchar(10) | NO | | NULL | |
| age | int(3) | YES | | NULL | |
+---------+-------------+------+-----+---------+-------+
4 rows in set (0.01 sec) # 8、添加主键（和删除主键挪移了位置，因为不想新增一个表）
mysql> alter table student10
-> modify name varchar(10) not null primary key;
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0 mysql> describe student10;
+---------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| id | int(11) | NO | | NULL | |
| name | varchar(10) | NO | PRI | NULL | |
| stu_num | varchar(10) | NO | | NULL | |
| age | int(3) | YES | | NULL | |
+---------+-------------+------+-----+---------+-------+
4 rows in set (0.01 sec) # 9、添加主键和自动增长（多主键是不允许的，主键是唯一，非空的但是可以多个字段联合成一个主键）
mysql> alter table student10
-> modify id int not null primary key auto_increment;
ERROR 1068 (42000): Multiple primary key defined
mysql> alter table student10
-> drop primary key;
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0 mysql> alter table student1
-> modify id int not null primary key auto_increment;
ERROR 1146 (42S02): Table 'db2.student1' doesn't exist
mysql> alter table student10
-> modify id int not null primary key auto_increment; # 添加主键和自动增长成功
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0 mysql> describe student10;
+---------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(10) | NO | | NULL | |
| stu_num | varchar(10) | NO | | NULL | |
| age | int(3) | YES | | NULL | |
+---------+-------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)
示例和练习
八、复制表
1、复制表结构+记录
key不会复制：主键、外键和索引。
create table t1 select host,user from mysql.user;
mysql> select host, user from mysql.user;
+-----------+---------------+
| host | user |
+-----------+---------------+
| localhost | mysql.session |
| localhost | mysql.sys |
| localhost | root |
+-----------+---------------+
3 rows in set (0.00 sec) mysql> create table t1 select host,user from mysql.user; # 查询出结果不输出屏幕直接传给新表
Query OK, 3 rows affected (0.02 sec)
Records: 3 Duplicates: 0 Warnings: 0 mysql> select * from t1;
+-----------+---------------+
| host | user |
+-----------+---------------+
| localhost | mysql.session |
| localhost | mysql.sys |
| localhost | root |
+-----------+---------------+
3 rows in set (0.00 sec) mysql> desc t1; # 查看key是否复制
+-------+----------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+----------+------+-----+---------+-------+
| host | char(60) | NO | | | |
| user | char(32) | NO | | | |
+-------+----------+------+-----+---------+-------+
2 rows in set (0.00 sec)
2、只复制表结构
方法一：故意设置一个不成立的条件
mysql> select host,user from mysql.user where 1>5; # 条件不成立，查不到任何数据
Empty set (0.00 sec) mysql> create table t2 select host,user from mysql.user where 1>5;
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0 mysql> desc t2;
+-------+----------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+----------+------+-----+---------+-------+
| host | char(60) | NO | | | |
| user | char(32) | NO | | | |
+-------+----------+------+-----+---------+-------+
2 rows in set (0.00 sec)
方法二：利用like
create table t3 like mysql.user;
mysql> create table t3 like mysql.user;
Query OK, 0 rows affected (0.03 sec) mysql> desc t3;
+------------------------+-----------------------------------+------+-----+-----------------------+-------+
| Field | Type | Null | Key | Default | Extra |
+------------------------+-----------------------------------+------+-----+-----------------------+-------+
| Host | char(60) | NO | PRI | | |
| User | char(32) | NO | PRI | | |
| Select_priv | enum('N','Y') | NO | | N | |
| Insert_priv | enum('N','Y') | NO | | N | |
| Update_priv | enum('N','Y') | NO | | N | |
| Delete_priv | enum('N','Y') | NO | | N | |
| Create_priv | enum('N','Y') | NO | | N | |
| Drop_priv | enum('N','Y') | NO | | N | |
| Reload_priv | enum('N','Y') | NO | | N | |
| Shutdown_priv | enum('N','Y') | NO | | N | |
| Process_priv | enum('N','Y') | NO | | N | |
| File_priv | enum('N','Y') | NO | | N | |
| Grant_priv | enum('N','Y') | NO | | N | |
| References_priv | enum('N','Y') | NO | | N | |
| Index_priv | enum('N','Y') | NO | | N | |
| Alter_priv | enum('N','Y') | NO | | N | |
| Show_db_priv | enum('N','Y') | NO | | N | |
| Super_priv | enum('N','Y') | NO | | N | |
| Create_tmp_table_priv | enum('N','Y') | NO | | N | |
| Lock_tables_priv | enum('N','Y') | NO | | N | |
| Execute_priv | enum('N','Y') | NO | | N | |
| Repl_slave_priv | enum('N','Y') | NO | | N | |
| Repl_client_priv | enum('N','Y') | NO | | N | |
| Create_view_priv | enum('N','Y') | NO | | N | |
| Show_view_priv | enum('N','Y') | NO | | N | |
| Create_routine_priv | enum('N','Y') | NO | | N | |
| Alter_routine_priv | enum('N','Y') | NO | | N | |
| Create_user_priv | enum('N','Y') | NO | | N | |
| Event_priv | enum('N','Y') | NO | | N | |
| Trigger_priv | enum('N','Y') | NO | | N | |
| Create_tablespace_priv | enum('N','Y') | NO | | N | |
| ssl_type | enum('','ANY','X509','SPECIFIED') | NO | | | |
| ssl_cipher | blob | NO | | NULL | |
| x509_issuer | blob | NO | | NULL | |
| x509_subject | blob | NO | | NULL | |
| max_questions | int(11) unsigned | NO | | 0 | |
| max_updates | int(11) unsigned | NO | | 0 | |
| max_connections | int(11) unsigned | NO | | 0 | |
| max_user_connections | int(11) unsigned | NO | | 0 | |
| plugin | char(64) | NO | | mysql_native_password | |
| authentication_string | text | YES | | NULL | |
| password_expired | enum('N','Y') | NO | | N | |
| password_last_changed | timestamp | YES | | NULL | |
| password_lifetime | smallint(5) unsigned | YES | | NULL | |
| account_locked | enum('N','Y') | NO | | N | |
+------------------------+-----------------------------------+------+-----+-----------------------+-------+
45 rows in set (0.00 sec) mysql> select * from t3;
Empty set (0.01 sec)
create table t3 like mysql.user;
九、删除表
DROP TABLE 表名;
mysql> drop table t2;
Query OK, 0 rows affected (0.01 sec) mysql> show tables;
+---------------+
| Tables_in_db3 |
+---------------+
| t1 |
+---------------+
1 row in set (0.00 sec)
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