The role of the index
设置了合适的索引之后，数据库利用各种快速的定位技术，能够大大加快查询速率；
特别是当表很大时，或者查询涉及到多个表时，使用索引可使查询加快成千倍；
可以降低数据库的IO成本，并且索引还可以降低数据库的排序成本；
通过创建唯一性索引保证数据表数据的唯一性；
可以加快表与表之间的连接；
在使用分组和排序时，可大大减少分组和排序时间；1, access to the database, create a database, create tables
[root@master2 ~]# mysql -uroot -p ##进入数据库
Enter password: ##输入密码
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql> create database school; ##创建数据库school
Query OK, 1 row affected (0.00 sec)
mysql> use school; ##使用数据库
Database changed
mysql> create table info( ##创建表
-> id int(4) not null primary key auto_increment, ##设置主键，自动增加
-> name varchar(10) not null, ##名字类型varchar不为空
-> address varchar(50) default 'nanjing', ##默认南京
-> age int(3) not null);
Query OK, 0 rows affected (0.02 sec)2, insert data into the table
mysql> insert into info (name,address,age) values ('zhangsan','beijing',20),('lisi','shanghai',22);
##插入数据
Query OK, 2 rows affected (0.01 sec)
Records: 2 Duplicates: 0 Warnings: 0
mysql> select * from info; ##查看表内容
+----+----------+----------+-----+
| id | name | address | age |
+----+----------+----------+-----+
| 1 | zhangsan | beijing | 20 |
| 2 | lisi | shanghai | 22 |
+----+----------+----------+-----+
2 rows in set (0.00 sec)
mysql> desc info; ##查看表结构
+---------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+----------------+
| id | int(4) | NO | PRI | NULL | auto_increment |
| name | varchar(10) | NO | | NULL | |
| address | varchar(50) | YES | | nanjing | |
| age | int(3) | NO | | NULL | |
+---------+-------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)3, using the create, alter, create a table directly defined in three ways to create an index (the general index, the unique index)
mysql> create index index_age on info (age); ##创建普通索引
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> show index from info; ##查看表中的索引
+-------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| info | 0 | PRIMARY | 1 | id | A | 2 | NULL | NULL | | BTREE | | |
| info | 1 | index_age | 1 | age | A | 2 | NULL | NULL | | BTREE | | |
+-------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
2 rows in set (0.00 sec)
mysql> drop index index_age on info; ##删除表中的索引
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> show index from info; ##查看表中的索引
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| info | 0 | PRIMARY | 1 | id | A | 2 | NULL | NULL | | BTREE | | |
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
1 row in set (0.01 sec)
mysql> create unique index unique_name on info (name); ##创建唯一性索引
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> show index from info; ##查看表中索引
+-------+------------+-------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-------+------------+-------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| info | 0 | PRIMARY | 1 | id | A | 2 | NULL | NULL | | BTREE | | |
| info | 0 | unique_name | 1 | name | A | 2 | NULL | NULL | | BTREE | | |
+-------+------------+-------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
2 rows in set (0.00 sec)
mysql> drop index unique_name on info; ##删除表中的索引
Query OK, 0 rows affected (0.00 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> show index from info; ##查看表中的索引
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| info | 0 | PRIMARY | 1 | id | A | 2 | NULL | NULL | | BTREE | | |
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
1 row in set (0.00 sec)
mysql> alter table info add unique index index_name (name); ##使用alter插入表索引
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> show index from info; ##查看表中的索引
+-------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| info | 0 | PRIMARY | 1 | id | A | 2 | NULL | NULL | | BTREE | | |
| info | 0 | index_name | 1 | name | A | 2 | NULL | NULL | | BTREE | | |
+-------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
2 rows in set (0.00 sec)4, create two tables, association, multi-table query
mysql> create table user( ##创建user表
-> id int(4) not null primary key auto_increment, ##设置主键和自动增加
-> name varchar(10) not null,
-> score decimal not null,
-> hobby int(2) not null default '1', ##默认1
-> index index_score (score)); ##设置索引score
Query OK, 0 rows affected (0.01 sec)
mysql> desc user; ##查看表结构
+-------+---------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------------+------+-----+---------+----------------+
| id | int(4) | NO | PRI | NULL | auto_increment |
| name | varchar(10) | NO | | NULL | |
| score | decimal(10,0) | NO | MUL | NULL | |
| hobby | int(2) | NO | | 1 | |
+-------+---------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)
mysql> insert into user (name,score,hobby) values ('test01',88,1),('stu01',99,2),('wangwu',77,3);
##向表中插入数据
Query OK, 3 rows affected (0.00 sec)
Records: 3 Duplicates: 0 Warnings: 0
mysql> select * from user; ##查看表内容
+----+--------+-------+-------+
| id | name | score | hobby |
+----+--------+-------+-------+
| 1 | test01 | 88 | 1 |
| 2 | stu01 | 99 | 2 |
| 3 | wangwu | 77 | 3 |
+----+--------+-------+-------+
3 rows in set (0.00 sec)
mysql> create table hob( ##创建hob表
-> id int(2) not null primary key,
-> hob_name varchar(10) not null);
Query OK, 0 rows affected (0.00 sec)
mysql> desc hob; ##查看表结构
+----------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+-------+
| id | int(2) | NO | PRI | NULL | |
| hob_name | varchar(10) | NO | | NULL | |
+----------+-------------+------+-----+---------+-------+
2 rows in set (0.00 sec)
mysql> insert into hob (id,hob_name) values (1,'看书'),(2,'运动'),(3,'听歌'); ##插入表数据
Query OK, 3 rows affected (0.00 sec)
Records: 3 Duplicates: 0 Warnings: 0
mysql> select * from hob; ##查看表内容
+----+----------+
| id | hob_name |
+----+----------+
| 1 | 看书 |
| 2 | 运动 |
| 3 | 听歌 |
+----+----------+
3 rows in set (0.00 sec)
mysql> select * from user inner join hob on user.hobby=hob.id; ##关联user和hob两张表
+----+--------+-------+-------+----+----------+
| id | name | score | hobby | id | hob_name |
+----+--------+-------+-------+----+----------+
| 1 | test01 | 88 | 1 | 1 | 看书 |
| 2 | stu01 | 99 | 2 | 2 | 运动 |
| 3 | wangwu | 77 | 3 | 3 | 听歌 |
+----+--------+-------+-------+----+----------+
3 rows in set (0.00 sec)
mysql> select user.name,hob.hob_name from user inner join hob on user.hobby=hob.id;
##去除其他内容显示name和hob_name内容
+--------+----------+
| name | hob_name |
+--------+----------+
| test01 | 看书 |
| stu01 | 运动 |
| wangwu | 听歌 |
+--------+----------+
3 rows in set (0.00 sec)
mysql> select u.name,h.hob_name from user u inner join hob h on u.hobby=h.id; ##设置简易名称
+--------+----------+
| name | hob_name |
+--------+----------+
| test01 | 看书 |
| stu01 | 运动 |
| wangwu | 听歌 |
+--------+----------+
3 rows in set (0.00 sec)
mysql> create view view_user as select u.name,h.hob_name from user u inner join hob h on u.hobby
##创建视图
Query OK, 0 rows affected (0.00 sec)
mysql> select * from view_user; ##查看视图
+--------+----------+
| name | hob_name |
+--------+----------+
| test01 | 看书 |
| stu01 | 运动 |
| wangwu | 听歌 |
+--------+----------+
3 rows in set (0.00 sec)
mysql> update user set hobby=3 where name='test01'; ##修改user表中内容
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select * from view_user; ##查看视图，即视图就是表的一个链接
+--------+----------+
| name | hob_name |
+--------+----------+
| stu01 | 运动 |
| test01 | 听歌 |
| wangwu | 听歌 |
+--------+----------+
3 rows in set (0.00 sec)5, full-text index, a composite index
mysql> select * from info; ##查看表内容
+----+----------+----------+-----+
| id | name | address | age |
+----+----------+----------+-----+
| 1 | zhangsan | beijing | 20 |
| 2 | lisi | shanghai | 22 |
+----+----------+----------+-----+
2 rows in set (0.00 sec)
mysql> show index from info; ##查看表的索引
+-------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| info | 0 | PRIMARY | 1 | id | A | 2 | NULL | NULL | | BTREE | | |
| info | 0 | index_name | 1 | name | A | 2 | NULL | NULL | | BTREE | | |
+-------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
2 rows in set (0.00 sec)
mysql> create fulltext index full_addr on info (address); ##以address创建全文索引
Query OK, 0 rows affected, 1 warning (0.07 sec)
Records: 0 Duplicates: 0 Warnings: 1
mysql> show index from info; ##查看表索引
+-------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| info | 0 | PRIMARY | 1 | id | A | 2 | NULL | NULL | | BTREE | | |
| info | 0 | index_name | 1 | name | A | 2 | NULL | NULL | | BTREE | | |
| info | 1 | full_addr | 1 | address | NULL | 2 | NULL | NULL | YES | FULLTEXT | | |
+-------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
3 rows in set (0.00 sec)
mysql> select * from user; ##查看user表内容
+----+--------+-------+-------+
| id | name | score | hobby |
+----+--------+-------+-------+
| 1 | test01 | 88 | 3 |
| 2 | stu01 | 99 | 2 |
| 3 | wangwu | 77 | 3 |
+----+--------+-------+-------+
3 rows in set (0.00 sec)
mysql> create index index_name_score on user (name,score); ##创建name和score的组合索引
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> show index from user; ##查看表索引
+-------+------------+------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-------+------------+------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| user | 0 | PRIMARY | 1 | id | A | 3 | NULL | NULL | | BTREE | | |
| user | 1 | index_score | 1 | score | A | 3 | NULL | NULL | | BTREE | | |
| user | 1 | index_name_score | 1 | name | A | 3 | NULL | NULL | | BTREE | | |
| user | 1 | index_name_score | 2 | score | A | 3 | NULL | NULL | | BTREE | | |
+-------+------------+------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
4 rows in set (0.00 sec)Features affairs
Atomic:
A transaction is a complete operation, each element of the transaction is indivisible (atoms)
of all elements of the transaction as a whole must be committed or rolled back
if any element in the transaction fails, the entire transaction fails
consistency:
when the transaction is completed, the data must be in a consistent state: before the beginning of the transaction, the data stored in the database in a consistent state; in the ongoing transaction, data may be in an inconsistent state; when the transaction is completed successfully, the data must go back again known consistent state of
isolation:
all concurrent transactions to modify the data are isolated from each other, indicating that the transaction must be independent, he should not in any way affect or depend on other matters
transaction to modify the data can be used in another after the end of the transaction to access the same data access transactions before the start of the data, or re-use the same data to another data
persistence:
transaction durability means that regardless of whether the system is a failure, the result of the transaction are permanent
once the transaction is committed , the effect of the transaction will be permanently reserved Database
1, open, inserted into the data table
mysql> select * from info; ##查看表内容数据
+----+----------+----------+-----+
| id | name | address | age |
+----+----------+----------+-----+
| 1 | zhangsan | beijing | 20 |
| 2 | lisi | shanghai | 22 |
+----+----------+----------+-----+
2 rows in set (0.00 sec)
mysql> insert into info (name,address,age) values ('wangwu','hangzhou',30)；##插入数据
mysql> begin; ##开启事务
Query OK, 0 rows affected (0.00 sec)
mysql> insert into info (name,address,age) values ('zhaoliu','hangzhou',31); ##插入数据
Query OK, 1 row affected (0.00 sec)
mysql> savepoint a; ##设置保存节点a
Query OK, 0 rows affected (0.00 sec)
mysql> select * from info; ##查看表数据
+----+----------+----------+-----+
| id | name | address | age |
+----+----------+----------+-----+
| 1 | zhangsan | beijing | 20 |
| 2 | lisi | shanghai | 22 |
| 3 | wangwu | hangzhou | 30 |
| 4 | zhaoliu | hangzhou | 31 |
+----+----------+----------+-----+
4 rows in set (0.00 sec)
mysql> insert into info (name,address,age) values ('tianqi','hangzhou',32); ##继续插入数据
Query OK, 1 row affected (0.00 sec)
mysql> savepoint b; ##设置保存节点b
Query OK, 0 rows affected (0.00 sec)
mysql> insert into info (name,address,age) values ('heiba','hangzhou',32); ##继续插入数据
Query OK, 1 row affected (0.00 sec)
mysql> select * from info; ##查看表内容
+----+----------+----------+-----+
| id | name | address | age |
+----+----------+----------+-----+
| 1 | zhangsan | beijing | 20 |
| 2 | lisi | shanghai | 22 |
| 3 | wangwu | hangzhou | 30 |
| 4 | zhaoliu | hangzhou | 31 |
| 5 | tianqi | hangzhou | 32 |
| 6 | heiba | hangzhou | 32 |
+----+----------+----------+-----+
6 rows in set (0.00 sec)2, use another terminal to see if successfully inserted
[root@master2 ~]# mysql -uroot -p ##进入数据库
Enter password: ##输入密码
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql> use school; ##使用数据库
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> select * from info; ##查看表内容，此时并没有提交
+----+----------+----------+-----+
| id | name | address | age |
+----+----------+----------+-----+
| 1 | zhangsan | beijing | 20 |
| 2 | lisi | shanghai | 22 |
| 3 | wangwu | hangzhou | 30 |
+----+----------+----------+-----+
3 rows in set (0.00 sec)3, rollback, return the saved node
mysql> rollback to b; ##利用回滚到保存节点b
Query OK, 0 rows affected (0.00 sec)
mysql> select * from info; ##查看表数据
+----+----------+----------+-----+
| id | name | address | age |
+----+----------+----------+-----+
| 1 | zhangsan | beijing | 20 |
| 2 | lisi | shanghai | 22 |
| 3 | wangwu | hangzhou | 30 |
| 4 | zhaoliu | hangzhou | 31 |
| 5 | tianqi | hangzhou | 32 |
+----+----------+----------+-----+
5 rows in set (0.00 sec)
mysql> rollback to a; ##回滚到保存节点a
Query OK, 0 rows affected (0.00 sec)
mysql> select * from info; ##查看表数据
+----+----------+----------+-----+
| id | name | address | age |
+----+----------+----------+-----+
| 1 | zhangsan | beijing | 20 |
| 2 | lisi | shanghai | 22 |
| 3 | wangwu | hangzhou | 30 |
| 4 | zhaoliu | hangzhou | 31 |
+----+----------+----------+-----+
4 rows in set (0.00 sec)
mysql> rollback; ##回滚到初始，退出事务状态
Query OK, 0 rows affected (0.00 sec)
mysql> select * from info; ##查看表数据
+----+----------+----------+-----+
| id | name | address | age |
+----+----------+----------+-----+
| 1 | zhangsan | beijing | 20 |
| 2 | lisi | shanghai | 22 |
| 3 | wangwu | hangzhou | 30 |
+----+----------+----------+-----+
3 rows in set (0.00 sec)4, commit the transaction
mysql> begin; ##开启事务
Query OK, 0 rows affected (0.00 sec)
mysql> insert into info (name,address,age) values ('heiba','hangzhou',32); ##插入数据
Query OK, 1 row affected (0.00 sec)
mysql> commit; ##提交事务
Query OK, 0 rows affected (0.00 sec)
mysql> select * from info; ##查看表数据
+----+----------+----------+-----+
| id | name | address | age |
+----+----------+----------+-----+
| 1 | zhangsan | beijing | 20 |
| 2 | lisi | shanghai | 22 |
| 3 | wangwu | hangzhou | 30 |
| 7 | heiba | hangzhou | 32 |
+----+----------+----------+-----+
4 rows in set (0.00 sec)5, the use of another terminal to view
mysql> select * from info; ##查看表数据
+----+----------+----------+-----+
| id | name | address | age |
+----+----------+----------+-----+
| 1 | zhangsan | beijing | 20 |
| 2 | lisi | shanghai | 22 |
| 3 | wangwu | hangzhou | 30 |
| 7 | heiba | hangzhou | 32 |
+----+----------+----------+-----+
4 rows in set (0.00 sec)6, another transaction mode of operation
mysql> set autocommit=0; ##设置不自动提交事务
Query OK, 0 rows affected (0.00 sec)
mysql> update info set address='beijing' where name='heiba'; ##修改表数据
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select * from info; ##查看表信息
+----+----------+----------+-----+
| id | name | address | age |
+----+----------+----------+-----+
| 1 | zhangsan | beijing | 20 |
| 2 | lisi | shanghai | 22 |
| 3 | wangwu | hangzhou | 30 |
| 7 | heiba | beijing | 32 |
+----+----------+----------+-----+
4 rows in set (0.00 sec)
##另一个终端查看
mysql> select * from info; ##查看表信息，并没有修改
+----+----------+----------+-----+
| id | name | address | age |
+----+----------+----------+-----+
| 1 | zhangsan | beijing | 20 |
| 2 | lisi | shanghai | 22 |
| 3 | wangwu | hangzhou | 30 |
| 7 | heiba | hangzhou | 32 |
+----+----------+----------+-----+
4 rows in set (0.00 sec)
mysql> set autocommit=1; ##开启自动提交事务
Query OK, 0 rows affected (0.00 sec)
##另一个终端查看
mysql> select * from info; ##查看表数据，此时就已经修改
+----+----------+----------+-----+
| id | name | address | age |
+----+----------+----------+-----+
| 1 | zhangsan | beijing | 20 |
| 2 | lisi | shanghai | 22 |
| 3 | wangwu | hangzhou | 30 |
| 7 | heiba | beijing | 32 |
+----+----------+----------+-----+
4 rows in set (0.00 sec)And InnoDB storage engine MyLSAM
1, view the system default storage engine
mysql> show engines; ##查看默认存储引擎innodb
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| Engine | Support | Comment | Transactions | XA | Savepoints |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| InnoDB | DEFAULT | Supports transactions, row-level locking, and foreign keys | YES | YES | YES |
mysql> show create table info; ##查看创建的表的存储引擎innodb
| info | CREATE TABLE "info" (
"id" int(4) NOT NULL AUTO_INCREMENT,
"name" varchar(10) NOT NULL,
"address" varchar(50) DEFAULT 'nanjing',
"age" int(3) NOT NULL,
PRIMARY KEY ("id"),
UNIQUE KEY "index_name" ("name"),
FULLTEXT KEY "full_addr" ("address")
) ENGINE=InnoDB AUTO_INCREMENT=8 DEFAULT CHARSET=utf82, modify the MySQL configuration file, set the default storage engine
[root@localhost ~]# vim /etc/my.cnf ##修改配置文件
[mysqld]
user = mysql
basedir = /usr/local/mysql
datadir = /usr/local/mysql/data
port = 3306
character_set_server=utf8
pid-file = /usr/local/mysql/mysql.pid
socket = /usr/local/mysql/mysql.sock
server-id = 1
default-storage-engine=Myisam ##添加默认存储引擎为Myisam
[root@master2 ~]# systemctl restart mysqld.service ##重启MySQL服务3, into the database
[root@master2 ~]# mysql -uroot -p ##进入数据库
Enter password: ##输入密码
mysql> use school; ##使用数据库
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 a ( id int ); ##创建一个a表
Query OK, 0 rows affected (0.00 sec)
mysql> show create table a; ##查看表默认的存储引擎Myisam
+-------+-------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+-------------------------------------------------------------------------------------+
| a | CREATE TABLE "a" (
"id" int(11) DEFAULT NULL
) ENGINE=MyISAM DEFAULT CHARSET=utf8 |
+-------+-------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
mysql> alter table a engine=innodb; ##修改表的存储引擎为innodb
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> show create table a; ##查看表的存储引擎innodb
+-------+-------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+-------------------------------------------------------------------------------------+
| a | CREATE TABLE "a" (
"id" int(11) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+-------+-------------------------------------------------------------------------------------+
1 row in set (0.00 sec)