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Mysql数据库理论基础之四 --- 表和索引的管理

时间:2017-06-03 19:19:45      阅读:276      评论:0      收藏:0      [点我收藏+]

标签:create delete alter indexes table

 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

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

| Charset  | Description     | Default collation   | Maxlen |

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

.......

| 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

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

| Collation      | Charset  | Id  | Default | Compiled | Sortlen |

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

| 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;

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

| Field | Type   | Null | Key | Default | Extra  |

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

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

| Couse | varchar(50) | NO   |  | NULL |     |

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

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

| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |

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

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

| test | 1 | Couse  |  1 | Couse | A  | NULL |  NULL | NULL |  | BTREE  |   |  |

2 rows in set (0.00 sec)

mysql> DESC test; #查看表结构

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

| Field | Type  | Null | Key | Default | Extra |

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

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

| Couse | varchar(50) | NO  | MUL | NULL    |    |

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

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

| Field  | Type  | Null | Key | Default | Extra  |

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

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

| Course | varchar(50) | NO   | MUL | NULL  |     |

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 ;

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

| Table | Non_unique | Key_name| Seq_in_index|Column_name|Collation|Cardinality| Sub_part | Packed | Null | Index_type | Comment | Index_comment |

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

| 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的索引   -B树索引

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

| Table| Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |

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

| 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

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

| Field | Type  | Null | Key | Default | Extra   |

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

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

| Couse | varchar(50) | NO   |   | NULL |     |

2 rows in set (0.00 sec)

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

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

| Field | Type  | Null | Key | Default | Extra |

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

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

| Couse | varchar(50) | NO  |    | NULL |    |

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

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

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

| Field | Type| Null | Key | Default | Extra |

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

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

| Couse | varchar(50)   | NO |    | NULL |   |

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;

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

| Field | Type | Null | Key | Default | Extra |

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

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

| Couse | varchar(50) | NO  |     | NULL    |     |

2 rows in set (0.00 sec)

mysql> DESC student;

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

| Field | Type | Null | Key | Default | Extra |

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

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

| Name | varchar(30)| YES |   | NULL |   |

| 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

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

|Table|Non_unique|Key_name|Seq_in_index|Column_name|Collation|Cardinality|Sub_part| Packed| Null| Index_type| Comment| Index_comment|

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

|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;

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

| Table| Non_unique| Key_name| Seq_in_index| Column_name| Collation| Cardinality| Sub_part | Packed | Null| Index_type| Comment| Index_comment |

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

| 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---

本文出自 “风过无痕” 博客,请务必保留此出处http://wangfx.blog.51cto.com/1697877/1931953

Mysql数据库理论基础之四 --- 表和索引的管理

标签:create delete alter indexes table

原文地址:http://wangfx.blog.51cto.com/1697877/1931953

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