Mysql数据库理论基础之四 --- 表和索引的管理

一、简介

由MySQL AB公司开发，是最流行的开放源码SQL数据库管理系统，主要特点：

1、是一种数据库管理系统
2、是一种关联数据库管理系统
3、是一种开放源码软件，且有大量可用的共享MySQL软件
4、MySQL数据库服务器具有快速、可靠和易于使用的特点
5、MySQL服务器工作在客户端/服务器模式下，或嵌入式系统中

二、MySQL 存储引擎，也称表类型

2.1. 单字段：

PRIMARY KEY 主键

UNIQUE KEY 唯一键

2.2 单或者多字段：

PRIMARY KEY(col,...)

UNIQUE KEY(col,...)

INDEX(col,...)

2.3 数据类型：

BIT[(length)] 比特

| TINYINT[(length)] [UNSIGNED] [ZEROFILL] 非常小的整数（1字节）

| SMALLINT[(length)] [UNSIGNED] [ZEROFILL] 小的整数（2字节）

| MEDIUMINT[(length)] [UNSIGNED] [ZEROFILL] 中等的整数（3字节）

| INT[(length)] [UNSIGNED] [ZEROFILL] 整数（4字节）

| INTEGER[(length)] [UNSIGNED] [ZEROFILL] 整数（4字节）相当于INT

| BIGINT[(length)] [UNSIGNED] [ZEROFILL] 大的整数（8个字节）

| REAL[(length,decimals)] [UNSIGNED] [ZEROFILL] 实数

| DOUBLE[(length,decimals)] [UNSIGNED] [ZEROFILL] 双精度整型

| FLOAT[(length,decimals)] [UNSIGNED] [ZEROFILL] 浮点型

| DECIMAL[(length[,decimals])] [UNSIGNED] [ZEROFILL]十进制小数点型

| NUMERIC[(length[,decimals])] [UNSIGNED] [ZEROFILL]数值型

时间：

| DATE 日期型

| TIME 时间型

| TIMESTAMP 时区型

| DATETIME 日期时间型

| YEAR 年

| CHAR[(length)] 定长字符型 255 characters

VARCHAR(length) 变长字符型 65535 characters

[CHARACTER SET charset_name] [COLLATE collation_name]

| BINARY[(length)] 二进制数

| VARBINARY(length) 变长二进制数

| TINYBLOB 非常小的大对数

| BLOB 大对数

| MEDIUMBLOB 中等的大对数

| LONGBLOB 长的大对数

文本：（不大小写）

| TINYTEXT [BINARY] 非常小的文本串 255 characters 2~8

[CHARACTER SET charset_name] [COLLATE collation_name]

| TEXT [BINARY] 文本串 65535 characters 2~16

[CHARACTER SET charset_name] [COLLATE collation_name]

| MEDIUMTEXT [BINARY] 中等的文本串 16,777,215 characters 2~24

[CHARACTER SET charset_name] [COLLATE collation_name]

| LONGTEXT [BINARY] 长的文本串 4,294,967,295 characters 2~32

[CHARACTER SET charset_name] [COLLATE collation_name]

| ENUM(value1,value2,value3,...) 枚举型

[CHARACTER SET charset_name] [COLLATE collation_name]

| SET(value1,value2,value3,...) 集合型

[CHARACTER SET charset_name] [COLLATE collation_name]

| spatial_type 空间的类型

2.4、创建数据库：

CREATE DATABASE|SCHEMA [IF NOT EXISTS] db_name [CHARACTER SET=] [COLLATE]

创建数据库可以设置字符集，排序规则

mysql> SHOW CHARACTER SET; #查看字符集

+----------+-----------------------------+---------------------+--------+

+----------+-----------------------------+---------------------+--------+

.......

| big5 | Big5 Traditional Chinese | big5_chinese_ci | 2 |

| tis620 | TIS620 Thai | tis620_thai_ci | 1 |

| cp1250 | Windows Central European | cp1250_general_ci | 1 |

| gbk | GBK Simplified Chinese | gbk_chinese_ci | 2 |

........

39 rows in set (0.00 sec)

mysql> SHOW COLLATION; #查看排序规则

+-------------------+----------+-----+---------+----------+---------+

+-------------------+----------+-----+---------+----------+---------+

| big5_chinese_ci | big5 | 1 | Yes | Yes | 1 |

| big5_bin | big5 | 84 | | Yes | 1 |

| cp1250_polish_ci | cp1250 | 99 | | Yes | 1 |

...

197 rows in set (0.00 sec)

mysql> show global variables like '%char%';

+------------------+-----------------+

| Variable_name | Value |

+------------------+----------------+

| character_set_client | latin1 |

| character_set_connection | latin1 |

| character_set_database | latin1 |

| character_set_filesystem | binary |

| character_set_results | latin1|

| character_set_server | latin1 |

| character_set_system | utf8 |

| character_sets_dir | /usr/share/mysql/charsets/ |

8 rows in set (0.00 sec)

mysql> CREATE DATABASE IF NOT EXISTS students CHARACTER SET 'gbk' COLLATE 'gbk_chinese_ci';

#创建一个students数据库，字符集为gbk，排序规则为gbk_chinese_ci

Query OK, 1 row affected (0.01 sec)

mysql> \q

Bye

[root@lamp ~]# ls /mydata/data #查看students是否新建成功

ib_logfile1 mysql-bin.000001 mysql-bin.000006 mysql-bin.000011 students

[root@lamp ~]# file /mydata/data/students/db.opt #查看students数据库中db.opt文件类型

/mydata/data/students/db.opt: ASCII text

2.5、修改数据库：

ALTER {DATABASE | SCHEMA} [db_name] alter_specification ...#修改数据库的属性，比如字符集或者排序规则，alter_specification CHARACTER SET = charset_name COLLATE = collation_name

alter_specification包含:

[DEFAULT] CHARACTER SET [=] charset_name

| [DEFAULT] COLLATE [=] collation_name

ALTER {DATABASE | SCHEMA} db_name UPGRADE DATA DIRECTORY NAME #升级数据库的数据目录

2.6、删除数据库：

DROP {DATABASE | SCHEMA} [IF EXISTS] db_name #删除数据库

2.7、创建表：

2.7.1.直接定义一张空表；col_name 字段名称 col_defination 字段定义

CREATE TABLE [IF NOT EXISTS] tb_name (col_name col_defination,)

col_defination字段定义包含：data_type字段类型

data_type [NOT NULL | NULL] [DEFAULT default_value]

[AUTO_INCREMENT] [UNIQUE [KEY] | [PRIMARY] KEY]

[COMMENT 'string']

[COLUMN_FORMAT {FIXED|DYNAMIC|DEFAULT}]

[STORAGE {DISK|MEMORY|DEFAULT}]

[reference_definition]

Usage:CREATE TABLE tb1(id INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,Name CHAR(20) NOT NULL,Age TINYINT NOT NULL);

#创建一个表tb1，包含三个字段:

id字段为无符号(UNSIGNED)，非空(NOT NULL)，自动增长(AUTO_INCREMENT)，为主键(PRIMARY KEY)的整型.

Name字段为定长20(CHAR(20)),非空的字符型。

Age字段为非空的非常小的整型。

或者 CREATE TABLE tb2(id INT UNSIGNED NOT NULL AUTO_INCREMENT,Name CHAR(20) NOT NULL,Age TINYINT NOT NULL,PRIMARY KEY(id),Unique KEY (Name),INDEX(age)); #Unique KEY 唯一键，INDEX索引

2.7.2.从其他表中查询出数据，并以之创建新表；

CREATE TABLE testcourses SELECT * FROM courses WHERE CID <= 2;

#从courses表中查找CID小于等于2的数据，并作为新建testcourses表的内容。

2.7.3.以其他表为模板创建一个空表；

查看表索引：

SHOW INDEXES FROM courses; 显示制定表索引

查看表结构：

DESC tb_name; 查看表结构

mysql> DESC courses;

+-------+----------+------+-----+---------+----------------+

+-------+----------+------+-----+---------+----------------+

| CID | tinyint(3) unsigned | NO | PRI |NULL|auto_increment|

2 rows in set (0.00 sec)

2.8、修改表定义：ALTER TABLE

添加、删除、修改字段，添加、删除、修改索引，改表名，修改表属性。

mysql> ALTER TABLE test ADD INDEX(Couse); #给test表增加以Couse字段为索引

Query OK, 0 rows affected (0.01 sec)

Records: 0 Duplicates: 0 Warnings: 0

mysql> SHOW INDEXES FROM test; #查看test表的索引

+------+-------+-------+------+------+-------+-------+-------+------+------+-------+-------+-------+

+------+-------+-------+------+------+-------+-------+

| test | 0 | PRIMARY | 1 | CID | A | 0 | NULL | NULL | | BTREE | | |

2 rows in set (0.00 sec)

mysql> DESC test; #查看表结构

+-------+---------------------+------+-----+---------+----------------+

+-------+---------------------+------+

| CID | tinyint(3) unsigned | NO | PRI | NULL | auto_increment |

2 rows in set (0.00 sec)

mysql> ALTER TABLE test CHANGE Couse Course VARCHAR(50) NOT NULL; #修改test表的Couse字段名称为Course并定义为变长50字符长度，非空

Query OK, 0 rows affected (0.01 sec)

Records: 0 Duplicates: 0 Warnings: 0

mysql> DESC test; 查看表结构

+--------+---------------------+------+-----+---------+----------------+

+--------+---------------------+------+

| CID | tinyint(3) unsigned | NO | PRI | NULL | auto_increment |

2 rows in set (0.00 sec)

mysql> DROP TABLE testcourses; #删除testcourses表

Query OK, 0 rows affected (0.00 sec)

mysql> SHOW TABLES;查看所有表

+--------------------+

| Tables_in_students |

+--------------------+

| courses |

| test |

+--------------------+

2 rows in set (0.00 sec)

mysql> ALTER TABLE test RENAME TO testcourses; #修改test表的名称为testcourses

Query OK, 0 rows affected (0.00 sec)

mysql> SHOW TABLES;查看所有表

+--------------------+

| Tables_in_students |

+--------------------+

| courses |

| testcourses |

2 rows in set (0.00 sec)

mysql> RENAME TABLE testcourses TO test; #也可以直接使用RENAME重命名。

Query OK, 0 rows affected (0.00 sec)

2.9、新增索引：（索引只能新建删除，不能修改）

CREATE INDEX index_name ON tb_name (col,...) col_name (length) ASC|DESC

指定以字段前几的长度为索引，ASC升序排列，DESC降序排列。

在tb_name表上的col字段创建一个索引index_name

CREATE INDEX name_on_student ON student (Name) USING BTREE;

#在student表中Name字段上建立一个名为name_on_student索引，类型为BTREE索引，默认为BTREE类型。

mysql> CREATE INDEX name_on_student ON student (Name) USING BTREE ;

mysql> SHOW INDEXES FROM student ;

+---------+------------+-----------------+--------------+-------------+-----------+-------------+

+---------+------------+-----------------+--------------+

| student | 0 | PRIMARY | 1 | SID | A| 4 |NULL | NULL| | BTREE| | |

| student | 1 |foreign_cid| 1 | CID | A| 4 |NULL | NULL| | BTREE | | |

| student | 1 |name_on_student| 1 | Name| A| 4 | NULL | NULL| YES| BTREE | | |

3 rows in set (0.00 sec)

mysql> DROP INDEX name_on_student ON student;#删除student表中的索引name_on_student

Query OK, 0 rows affected (0.04 sec)

Records: 0 Duplicates: 0 Warnings: 0

mysql> CREATE INDEX name_on_student ON student (Name(5) DESC);#为student表以Name字段

的前5个字符建立一个降序（DESC）排列的索引.

Query OK, 0 rows affected (0.05 sec)

Records: 0 Duplicates: 0 Warnings: 0

实例1：创建一个students数据库，以及表的创建，查找等功能的练习；

1.1.创建一个students数据库

mysql> CREATE DATABASE IF NOT EXISTS students CHARACTER SET 'gbk' COLLATE 'gbk_chinese_ci';

#字符集为gbk，排序规则为gbk_chinese_ci

Query OK, 1 row affected (0.01 sec)

mysql> USE students;

Database changed

mysql> CREATE TABLE courses(CID TINYINT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,Couse VARCHAR(50) NOT NULL);

Query OK, 0 rows affected (0.07 sec)

mysql> SHOW TABLE STATUS LIKE 'courses'\G;

************************ 1. row ***********************

Name: courses

Engine: InnoDB #数据库引擎

Version: 10

Row_format: Compact #类似压缩格式存储

Rows: 0

Avg_row_length: 0

Data_length: 16384

...

1.2.删除表，新建引擎为MyISAM的新表

mysql> DROP TABLES courses; #删除表

Query OK, 0 rows affected (0.01 sec)

mysql> CREATE TABLE courses(CID TINYINT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,Couse VARCHAR(50) NOT NULL) ENGINE=MyISAM; #ENGINE设定引擎为MyISAM

Query OK, 0 rows affected (0.00 sec)

mysql> SHOW TABLE STATUS LIKE 'courses' \G;

*************** 1. row *************

Name: courses

Engine: MyISAM

Version: 10

Row_format: Dynamic

Rows: 0

Avg_row_length: 0

Data_length: 0

Max_data_length: 281474976710655

...

1 row in set (0.00 sec)

1.3.1新表中加入值

mysql> INSERT INTO courses (Couse) values ('physics'),('english'),('chemistry'),('maths');

#插入Couse课程字段数据，添加物理，英语，化学，数学等课程。

Query OK, 4 rows affected (0.00 sec)

Records: 4 Duplicates: 0 Warnings: 0

mysql> SELECT * FROM courses; #查询courses表的条目

+-----+-----------+

| CID | Couse |

+-----+-----------+

| 1 | physics |

| 2 | english |

| 3 | chemistry|

| 4 | maths |

+-----+-----------+

4 rows in set (0.00 sec)

mysql> SHOW INDEXES FROM courses; #查看courses表的索引 -B树索引

+---------+------------+----------+--------------+

+---------+------------+----------+--------------+

| courses | 0 | PRIMARY | 1 | CID | A | 4 | NULL | NULL | | BTREE | | |

1 row in set (0.00 sec)

1.3.2新表中加入查询值，但生成的表与原表格式会不一致，可先创建表再插入值；

mysql> CREATE TABLE testcourses SELECT * FROM courses WHERE CID <= 2;

#查找courses表中CID字段小于等于2的数据，并把查找到的数据作为新建testcourses表的数据内容。

Query OK, 2 rows affected (0.08 sec)

Records: 2 Duplicates: 0 Warnings: 0

mysql> SHOW TABLES; #查看当前数据库表的信息

+--------------------+

| Tables_in_students |

+--------------------+

| courses |

| testcourses |

+--------------------+

2 rows in set (0.00 sec)

mysql> SELECT * FROM testcourses; #查看testcourses表的内容

+-----+---------+

| CID | Couse |

+-----+---------+

| 1 | physics |

| 2 | english |

+-----+---------+

2 rows in set (0.00 sec)

mysql> DESC courses; #查看courses表结构

+-------+---------------------+------+-----+---------+----------------+

+-------+---------------------+

| CID | tinyint(3) unsigned | NO | PRI | NULL| auto_increment |

2 rows in set (0.00 sec)

mysql> DESC testcourses; #查看testcourses表结构与上面的courses不一样

+-------+---------------------+------+-----+---------+-------+

+-------+---------------------+

| CID | tinyint(3) unsigned | NO | | 0 | |

+-------+---------------------+

2 rows in set (0.00 sec)

mysql> CREATE TABLE test LIKE courses; #以courses表为模板创建test空表。

Query OK, 0 rows affected (0.00 sec)

mysql> DESC test; #查看test表结构

+-------+---------------------+------+-----+---------+----------------+

+-------+---------------------+

| CID | tinyint(3) unsigned | NO | PRI | NULL | auto_increment |

2 rows in set (0.00 sec)

mysql> SHOW TABLE STATUS LIKE 'test'\G; #查看test表的状态

*************** 1. row *********

Name: test

Engine: MyISAM

Version: 10

Row_format: Dynamic

Rows: 0

Avg_row_length: 0

Data_length: 0

Max_data_length: 281474976710655

Index_length: 1024

Data_free: 0

Auto_increment: 1

Create_time: 2017-04-25 11:31:46

Update_time: 2017-04-25 11:31:46

Check_time: NULL

Collation: gbk_chinese_ci

Checksum: NULL

Create_options:

Comment:

1 row in set (0.00 sec)

实例2.建立student表，并进行相关数据的插入，查询操作练习，修改引擎，修改字段修饰，增加外键索引；

2.1.建立student表

mysql>CREATE TABLE student (SID INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,Name VARCHAR(30),CID INT NOT NULL);

#创建student表，包含3个字段，SID字段为无符号、非空、自动增长、主键的整数型，

Name字段为变长30字符，

CID字符为非空整数型。

mysql> SHOW TABLES;

+--------------------+

| Tables_in_students |

+--------------------+

| courses |

| student |

| testcourses |

3 rows in set (0.00 sec)

2.2.在student表中插入数据

mysql>INSERT INTO student (Name,CID) VALUES ('Li Li',1),('ChengChen',2); #对Name,CID字段插入2条数据。

Query OK, 2 rows affected (0.01 sec)

Records: 2 Duplicates: 0 Warnings: 0

mysql>SELECT * FROM student; #查询student表

+-----+------------+-----+

| SID | Name | CID |

+-----+------------+-----+

| 1 | Li Li | 1 |

| 2 | ChengChen | 2 |

2 rows in set (0.00 sec)

2.3.在student表中查询数据

mysql> SELECT * FROM courses; #查询courses表

+-----+-----+

| CID| Couse|

+-----+-----+

|1|physics|

|2|english|

|3|chemistry|

|4| maths|

|5| Hamagong|

|6| Pixiejianfa|

|7| Kuihuabaodian |

7 rows in set (0.00 sec)

mysql> SELECT Name,Couse FROM student,courses WHERE student.CID=courses.CID; #查询student表和courses表中CID相同的Name和Couse字段内容

+-----+------+

| Name|Couse|

+------+-----+

| Li Li| physics |

| Cheng Chen | english |

2 rows in set (0.00 sec)

2.4.在student表中删除、修改数据

mysql>DELETE FROM courses WHERE CID > 5; #删除SID大于5的行。

Query OK, 5 rows affected (0.01 sec)

mysql>ALTER TABLE courses ENGINE=Innodb; #修改courses表的引擎为Innodb;

Query OK, 4 rows affected (0.03 sec)

Records: 4 Duplicates: 0 Warnings: 0

mysql>ALTER TABLE student MODIFY CID TINYINT UNSIGNED NOT NULL;#修改student表中CID字段的修饰MODIFY

Query OK, 4 rows affected (0.02 sec)

Records: 4 Duplicates: 0 Warnings: 0

mysql> DESC courses;

+-----+--------+------+-----+---------+-----------+

+-------+----------+

| CID | tinyint(3) unsigned | NO | PRI |NULL | auto_increment |

2 rows in set (0.00 sec)

mysql> DESC student;

+-------+--------+------+-----+---------+-----------+

+-------+------------+

| SID | int(10) unsigned | NO | PRI | NULL | auto_increment |

| CID | tinyint(3) unsigned | NO | | NULL | |

3 rows in set (0.00 sec)

mysql> ALTER TABLE student ADD FOREIGN KEY foreign_cid (CID) REFERENCES courses (CID);

#为student表的CID字段增加一个外键foreign_cid关联courses表的CID字段。

Query OK, 4 rows affected (0.03 sec)

Records: 4 Duplicates: 0 Warnings: 0

mysql> SHOW INDEXES FROM student; #查看student表的索引

+---------+------------+----------+-----------+----------+---------+----------+

+---------+------------+------------+

|student |0 | PRIMARY | 1 | SID | A|2 |NULL | NULL| | BTREE| | |

|student |1 |foreign_cid| 1 | CID | A|2 |NULL | NULL| | BTREE| | |

2 rows in set (0.00 sec)

mysql> INSERT INTO student (Name,CID) VALUES ('Guo Xiang',5);

ERROR 1452 (23000): Cannot add or update a child row: a foreign key constraint fails (`students`.`student`, CONSTRAINT `student_ibfk_1` FOREIGN KEY (`CID`) REFERENCES `courses` (`CID`))

#提示报错，由于CID外键索引courses表中CID没有5，所以无法增加。

mysql> ALTER TABLE student AUTO_INCREMENT=5; #设定student表下一条数据的自动增长主键SID从5开始增长。

Query OK, 4 rows affected (0.05 sec)

Records: 4 Duplicates: 0 Warnings: 0

mysql> SELECT * FROM student; #查询表的内容

+-----+----------+-----+

| SID | Name| CID |

+-----+--------+-----+

| 1 | Li Lianjie | 1 |

| 2 | Cheng Long | 2 |

| 3 | Xiao Longnv | 3 |

| 4 | Yang Guo | 4 |

4 rows in set (0.00 sec)

mysql> INSERT INTO student (Name,CID) VALUES ('Guo Xiang',3);

#插入一条数据，SID主键由于上面设置从5开始增长，所以刚插入的数据是从5开始；

Query OK, 1 row affected (0.00 sec)

mysql> SELECT * FROM student;

+-----+----------+-----+

| SID | Name | CID |

+-----+-------------+-----+

| 1 | Li Lianjie| 1 |

| 2 | Cheng Long | 2 |

| 3 | Xiao Longnv | 3 |

| 4 | Yang Guo | 4 |

|5 | Guo Xiang | 3 |

5 rows in set (0.00 sec)

mysql> INSERT INTO student (Name,CID) VALUES ('Qiao Feng',2);插入数据

Query OK, 1 row affected (0.00 sec)

mysql> SELECT * FROM student;

mysql> DELETE FROM student WHERE SID >2 AND SID <5; #删除2<SID<5的行

Query OK, 2 rows affected (0.00 sec)

mysql> SELECT * FROM student; #验证

+-----+------------+-----+

| SID | Name | CID |

| 1 | Li Lianjie | 1 |

| 2 | Cheng Long | 2 |

| 5 | Guo Xiang | 3 |

| 6 | Qiao Feng | 2 |

4 rows in set (0.00 sec)

mysql> DELETE FROM student WHERE SID in (5,6); #删除SID为5和6的行

Query OK, 2 rows affected (0.00 sec)

mysql> SELECT * FROM student;

+-----+------------+-----+

| SID | Name | CID |

+-----+------------+-----+

| 1 | Li Lianjie | 1 |

| 2 | Cheng Long | 2 |

2 rows in set (0.00 sec)

mysql>ALTER TABLE student AUTO_INCREMENT=3;#设定表下一条数据的自动增长主键SID从3开始增长

Query OK, 2 rows affected (0.07 sec)

Records: 2 Duplicates: 0 Warnings: 0

mysql>INSERT INTO student (Name,CID) VALUES ('Yang Guo',3),('Guo Jing',4);#插入2条数据

Query OK, 2 rows affected (0.00 sec)

Records: 2 Duplicates: 0 Warnings: 0

mysql> SELECT * FROM student;

+-----+------------+-----+

| SID | Name | CID |

+-----+------------+-----+

| 1 | Li Lianjie | 1 |

| 2 | Cheng Long | 2 |

| 3 | Yang Guo | 3 |

| 4 | Guo Jing | 4 |

4 rows in set (0.00 sec)

2.5.在student表中创建索引，实现比较或排序

mysql> SELECT * FROM student;

+-----+------------+-----+

| SID | Name | CID |

+-----+------------+-----+

| 1 | Li Li | 1 |

| 2 | Cheng Chen | 2 |

| 3 | YangGuo | 3 |

| 4 | GuoJing | 4 |

4 rows in set (0.00 sec)

mysql> CREATE INDEX name_on_student ON student (Name) USING BTREE;

Query OK, 0 rows affected (0.09 sec)

Records: 0 Duplicates: 0 Warnings: 0

mysql> DROP INDEX name_on_student ON student; #索引只能新建或删除,因其是结构无法修改

Query OK, 0 rows affected (0.02 sec)

Records: 0 Duplicates: 0 Warnings: 0

mysql> CREATE INDEX name_on_student ON student (Name(5) DESC) USING BTREE;

Query OK, 0 rows affected (0.05 sec)

Records: 0 Duplicates: 0 Warnings: 0

mysql> SHOW INDEXES FROM student;

+---------+------------+-----------------+--------------+-------------+-----------+

+---------+------------+-----------------+

| student|0 | PRIMARY| 1 | SID | A | 2 | NULL | NULL | BTREE | | |

| student|1 | foreign_cid | 1| CID | A |2 | NULL | NULL| | BTREE | | |

| student|1 | name_on_student|1| Name| A |4 | 5 | NULL | YES| BTREE | | |

3 rows in set (0.00 sec)

---end-6---

来源：oschina

链接：https://my.oschina.net/u/4305379/blog/4343833

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