MySQL索引创建与删除
1.1 问题
本案例要求熟悉MySQL索引的类型及操作方法,主要练习以下任务:
- 普通索引、唯一索引、主键索引的创建/删除
- 自增主键索引的创建/删除
- 建立员工表yg、工资表gz,数据内容如表-1、表-2所示,设置外键实现同步更新与同步删除
表-1 员工表yg的数据
表-2 工资表gz的数据
1.2 步骤
实现此案例需要按照如下步骤进行。
步骤一:索引的创建与删除
创建表的时候指定INDEX索引字段
创建库home:
- mysql> create database home;
- Query OK, 1 row affected (0.00 sec)
允许有多个INDEX索引字段。比如,以下操作在home库中创建了tea4表,将其中的id、name作为索引字段:
- mysql> USE home;
- Database changed
- mysql> CREATE TABLE tea4(
- -> id char(6) NOT NULL,
- -> name varchar(6) NOT NULL,
- -> age int(3) NOT NULL,
- -> gender ENUM(‘boy‘,‘girl‘) DEFAULT ‘boy‘,
- -> INDEX(id),INDEX(name)
- -> );
- Query OK, 0 rows affected (0.59 sec)
查看新建tea4表的字段结构,可以发现两个非空索引字段的KEY标志为MUL:
- mysql> DESC tea4;
- +--------+--------------------+------+-----+---------+-------+
- | Field | Type | Null | Key | Default | Extra |
- +--------+--------------------+------+-----+---------+-------+
- | id | char(6) | NO | MUL | NULL | |
- | name | varchar(6) | NO | MUL | NULL | |
- | age | int(3) | NO | | NULL | |
- | gender | enum(‘boy‘,‘girl‘) | YES | | boy | |
- +--------+--------------------+------+-----+---------+-------+
- 4 rows in set (0.00 sec)
2)删除现有表的某个INDEX索引字段
比如,删除tea4表中名称为named的INDEX索引字段:
- mysql> drop INDEX name ON tea4; //删除name字段的索引
- Query OK, 0 rows affected (0.18 sec)
- Records: 0 Duplicates: 0 Warnings: 0
- mysql> DESC tea4; //确认删除结果
- +--------+--------------------+------+-----+---------+-------+
- | Field | Type | Null | Key | Default | Extra |
- +--------+--------------------+------+-----+---------+-------+
- | id | char(6) | NO | MUL | NULL | |
- | name | varchar(6) | NO | | NULL | |
- | age | int(3) | NO | | NULL | |
- | gender | enum(‘boy‘,‘girl‘) | YES | | boy | |
- +--------+--------------------+------+-----+---------+-------+
- 4 rows in set (0.00 sec)
3)在已有的某个表中设置INDEX索引字段
比如,针对tea4表的age字段建立索引,名称为 nianling:
- mysql> CREATE INDEX nianling ON tea4(age); //针对指定字段创建索引
- Query OK, 0 rows affected (0.62 sec)
- Records: 0 Duplicates: 0 Warnings: 0
- mysql> DESC tea4; //确认创建结果
- +--------+--------------------+------+-----+---------+-------+
- | Field | Type | Null | Key | Default | Extra |
- +--------+--------------------+------+-----+---------+-------+
- | id | char(6) | NO | MUL | NULL | |
- | name | varchar(6) | NO | | NULL | |
- | age | int(3) | NO | MUL | NULL | |
- | gender | enum(‘boy‘,‘girl‘) | YES | | boy | |
- +--------+--------------------+------+-----+---------+-------+
- 4 rows in set (0.00 sec)
4)查看指定表的索引信息
使用SHOW INDEX 指令:
- mysql> SHOW INDEX FROM tea4\G
- *************************** 1. row ***************************
- Table: tea4
- Non_unique: 1
- Key_name: id
- Seq_in_index: 1
- Column_name: id
- Collation: A
- Cardinality: 0
- Sub_part: NULL
- Packed: NULL
- Null:
- Index_type: BTREE //使用B树算法
- Comment:
- Index_comment:
- *************************** 2. row ***************************
- Table: tea4
- Non_unique: 1
- Key_name: nianling //索引名称
- Seq_in_index: 1
- Column_name: age //字段名称
- Collation: A
- Cardinality: 0
- Sub_part: NULL
- Packed: NULL
- Null:
- Index_type: BTREE
- Comment:
- Index_comment:
- 2 rows in set (0.00 sec)
5)创建表的时候指定UNIQUE索引字段
UNIQUE表示唯一性的意思,同一个表中可以有多个字段具有唯一性。
比如,创建tea5表,将id、name字段建立设置UNIQUE索引,age字段设置INDEX索引:
- mysql> CREATE TABLE tea5(
- -> id char(6),
- -> name varchar(4) NOT NULL,
- -> age int(3) NOT NULL,
- -> UNIQUE(id),UNIQUE(name),INDEX(age)
- -> );
- Query OK, 0 rows affected (0.30 sec)
查看新建tea5表的字段结构,可发现UNIQUE字段的KEY标志为UNI;另外,由于字段name必须满足“NOT NULL”的非空约束,所以将其设置为UNIQUE后会自动变成了PRIMARY KEY主键字段:
- mysql> DESC tea5; //确认设置结果
- +-------+------------+------+-----+---------+-------+
- | Field | Type | Null | Key | Default | Extra |
- +-------+------------+------+-----+---------+-------+
- | id | char(6) | YES | UNI | NULL | |
- | name | varchar(4) | NO | PRI | NULL | |
- | age | int(3) | NO | MUL | NULL | |
- +-------+------------+------+-----+---------+-------+
- 3 rows in set (0.03 sec)
6)删除UNIQUE索引、在已有的表中设置UNIQUE索引字段
先删除tea5表name字段的唯一索引(与删除INDEX索引的方法相同):
- mysql> DROP INDEX name ON tea5; //清除UNIQUE索引
- Query OK, 0 rows affected (0.97 sec)
- Records: 0 Duplicates: 0 Warnings: 0
- mysql> DESC tea5; //确认删除结果
- +-------+------------+------+-----+---------+-------+
- | Field | Type | Null | Key | Default | Extra |
- +-------+------------+------+-----+---------+-------+
- | id | char(6) | YES | UNI | NULL | |
- | name | varchar(4) | NO | | NULL | |
- | age | int(3) | NO | MUL | NULL | |
- +-------+------------+------+-----+---------+-------+
- 3 rows in set (0.00 sec)
重新为tea5表的name字段建立UNIQUE索引,并确认结果:
- mysql> CREATE UNIQUE INDEX name ON tea5(name); //建立UNIQUE索引
- Query OK, 0 rows affected (0.47 sec)
- Records: 0 Duplicates: 0 Warnings: 0
- mysql> DESC tea5; //确认设置结果
- +-------+------------+------+-----+---------+-------+
- | Field | Type | Null | Key | Default | Extra |
- +-------+------------+------+-----+---------+-------+
- | id | char(6) | YES | UNI | NULL | |
- | name | varchar(4) | NO | PRI | NULL | |
- | age | int(3) | NO | MUL | NULL | |
- +-------+------------+------+-----+---------+-------+
- 3 rows in set (0.00 sec)
7)建表时设置PRIMARY KEY主键索引
主键索引实际上在前面已经接触过了,建表的时候可以直接指定。如果表内一开始没有主键字段,则新设置的非空UNIQUE字段相当于具有PRIMARY KEY主键约束。
每个表中的主键字段只能有一个。
建表的时候,可以直接在某个字段的“约束条件”部分指定PRIMARY KEY;也可以在最后指定PRIMARY KEY(某个字段名)。比如:
- mysql> CREATE TABLE biao01(
- -> id int(4) PRIMARY KEY, //直接在字段定义时约束
- -> name varchar(8)
- -> );
- Query OK, 0 rows affected (0.19 sec)
或者:
- mysql> CREATE TABLE biao02(
- -> id int(4),
- -> name varchar(8),
- -> PRIMARY KEY(id) //所有字段定义完,最后指定
- -> );
- Query OK, 0 rows affected (0.17 sec)
在建表的时候,如果主键字段为int类型,还可以为其设置AUTO_INCREMENT自增属性,这样当添加新的表记录时,此字段的值会自动从1开始逐个增加,无需手动指定。比如,新建一个tea6表,将id列作为自增的主键字段:
- mysql> CREATE TABLE tea6(
- -> id int(4) AUTO_INCREMENT,
- -> name varchar(4) NOT NULL,
- -> age int(2) NOT NULL,
- -> PRIMARY KEY(id)
- -> );
- Query OK, 0 rows affected (0.29 sec)
8)删除现有表的PRIMARY KEY主键索引
如果要移除某个表的PRIMARY KEY约束,需要通过ALTER TABLE指令修改。比如,以下操作将清除biao01表的主键索引。
清除前(主键为id):
- mysql> DESC biao01;
- +-------+------------+------+-----+---------+-------+
- | Field | Type | Null | Key | Default | Extra |
- +-------+------------+------+-----+---------+-------+
- | id | int(4) | NO | PRI | NULL | |
- | name | varchar(8) | YES | | NULL | |
- +-------+------------+------+-----+---------+-------+
- 2 rows in set (0.00 sec)
清除操作:
- mysql> ALTER TABLE biao01 DROP PRIMARY KEY;
- Query OK, 0 rows affected (0.49 sec)
- Records: 0 Duplicates: 0 Warnings: 0
清除后(无主键):
- mysql> DESC biao01;
- +-------+------------+------+-----+---------+-------+
- | Field | Type | Null | Key | Default | Extra |
- +-------+------------+------+-----+---------+-------+
- | id | int(4) | NO | | NULL | |
- | name | varchar(8) | YES | | NULL | |
- +-------+------------+------+-----+---------+-------+
- 2 rows in set (0.00 sec)
当尝试删除tea6表的主键时,会出现异常:
- mysql> ALTER TABLE tea6 DROP PRIMARY KEY;
- ERROR 1075 (42000): Incorrect table definition; there can be only one auto column and it must be defined as a key
这是因为tea6表的主键字段id具有AUTO_INCREMNET自增属性,提示这种字段必须作为主键存在,因此若要清除此主键必须先清除自增属性——修改id列的字段定义:
- mysql> ALTER TABLE tea6 MODIFY id int(4) NOT NULL;
- Query OK, 0 rows affected (0.75 sec)
- Records: 0 Duplicates: 0 Warnings: 0
然后再清除主键属性就OK了:
- mysql> ALTER TABLE tea6 DROP PRIMARY KEY; //清除主键
- Query OK, 0 rows affected (0.39 sec)
- Records: 0 Duplicates: 0 Warnings: 0
- mysql> desc tea6; //确认清除结果
- +-------+------------+------+-----+---------+-------+
- | Field | Type | Null | Key | Default | Extra |
- +-------+------------+------+-----+---------+-------+
- | id | int(4) | NO | | NULL | |
- | name | varchar(4) | NO | | NULL | |
- | age | int(2) | NO | | NULL | |
- +-------+------------+------+-----+---------+-------+
- 3 rows in set (0.01 sec)
9)为现有表添加PRIMARY KEY主键索引
重新为tea6表指定主键字段,仍然使用id列:
- mysql> ALTER TABLE tea6 ADD PRIMARY KEY(id); //设置主键字段
- Query OK, 0 rows affected (0.35 sec)
- Records: 0 Duplicates: 0 Warnings: 0
- mysql> DESC tea6; //确认设置结果
- +-------+------------+------+-----+---------+-------+
- | Field | Type | Null | Key | Default | Extra |
- +-------+------------+------+-----+---------+-------+
- | id | int(4) | NO | PRI | NULL | |
- | name | varchar(4) | NO | | NULL | |
- | age | int(2) | NO | | NULL | |
- +-------+------------+------+-----+---------+-------+
- 3 rows in set (0.00 sec)
步骤二:创建数据库并设置外键实现同步更新与同步删除
根据实验任务要求,两个表格的字段结构如表-1、表-2所示。
1)创建yg表,用来记录员工工号、姓名
其中yg_id列作为主键,并设置自增属性
- mysql> CREATE TABLE yg(
- -> yg_id int(4) AUTO_INCREMENT,
- -> name char(16) NOT NULL,
- -> PRIMARY KEY(yg_id)
- -> );
- Query OK, 0 rows affected (0.15 sec)
2)创建gz表,用来记录员工的工资信息
其中gz_id需要参考员工工号,即gz表的gz_id字段设为外键,将yg表的yg_id字段作为参考键:
- mysql> CREATE TABLE gz(
- -> gz_id int(4) NOT NULL,
- -> name char(16) NOT NULL,
- -> gz float(7,2) NOT NULL DEFAULT 0,
- -> INDEX(name),
- -> FOREIGN KEY(gz_id) REFERENCES yg(yg_id)
- -> ON UPDATE CASCADE ON DELETE CASCADE
- -> );
- Query OK, 0 rows affected (0.23 sec)
3)为yg表添加2条员工信息记录
因yg_id有AUTO_INCREMENT属性,会自动填充,所以只要为name列赋值就可以了。
插入表记录可使用INSERT指令,这里先执行下列操作,具体在下一章学习:
- mysql> INSERT INTO yg(name) VALUES(‘Jerry‘),(‘Tom‘);
- Query OK, 2 rows affected (0.16 sec)
- Records: 2 Duplicates: 0 Warnings: 0
确认yg表的数据记录:
- mysql> SELECT * FROM yg;
- +-------+-------+
- | yg_id | name |
- +-------+-------+
- | 1 | Jerry |
- | 2 | Tom |
- +-------+-------+
- 2 rows in set (0.00 sec)
4)为gz表添加2条工资信息记录
同上,数据参考图-2,插入相应的工资记录(gz_id字段未指定默认值,也未设置自增属性,所以需要手动赋值):
- mysql> INSERT INTO gz(gz_id,name,gz)
- -> VALUES(1,‘Jerry‘,12000),(2,‘Tom‘,8000)
- -> ;
- Query OK, 2 rows affected (0.06 sec)
- Records: 2 Duplicates: 0 Warnings: 0
确认gz表的数据记录:
- mysql> SELECT * FROM gz;
- +-------+-------+----------+
- | gz_id | name | gz |
- +-------+-------+----------+
- | 1 | Jerry | 12000.00 |
- | 2 | Tom | 8000.00 |
- +-------+-------+----------+
- 2 rows in set (0.05 sec)
5)验证表记录的UPDATE更新联动
将yg表中Jerry用户的yg_id修改为1234:
- mysql> update yg SET yg_id=1234 WHERE name=‘Jerry‘;
- Query OK, 1 row affected (0.05 sec)
- Rows matched: 1 Changed: 1 Warnings: 0
确认修改结果:
- mysql> SELECT * FROM yg;
- +-------+-------+
- | yg_id | name |
- +-------+-------+
- | 2 | Tom |
- | 1234 | Jerry |
- +-------+-------+
- 2 rows in set (0.00 sec)
同时也会发现,gz表中Jerry用户的gz_id也跟着变了:
- mysql> SELECT * FROM gz;
- +-------+-------+----------+
- | gz_id | name | gz |
- +-------+-------+----------+
- | 1234 | Jerry | 12000.00 |
- | 2 | Tom | 8000.00 |
- +-------+-------+----------+
- 2 rows in set (0.00 sec)
6)验证表记录的DELETE删除联动
删除yg表中用户Jerry的记录:
- mysql> DELETE FROM yg WHERE name=‘Jerry‘;
- Query OK, 1 row affected (0.05 sec)
确认删除结果:
- mysql> SELECT * FROM yg;
- +-------+------+
- | yg_id | name |
- +-------+------+
- | 2 | Tom |
- +-------+------+
- 1 row in set (0.00 sec)
查看gz表中的变化(Jerry的记录也没了):
- mysql> SELECT * FROM gz;
- +-------+------+---------+
- | gz_id | name | gz |
- +-------+------+---------+
- | 2 | Tom | 8000.00 |
- +-------+------+---------+
- 1 row in set (0.00 sec)
7)删除指定表的外键约束
先通过SHOW指令获取表格的外键约束名称:
- mysql> SHOW CREATE TABLE gz\G
- *************************** 1. row ***************************
- Table: gz
- Create Table: CREATE TABLE `gz` (
- `gz_id` int(4) NOT NULL,
- `name` char(16) NOT NULL,
- `gz` float(7,2) NOT NULL DEFAULT ‘0.00‘,
- KEY `name` (`name`),
- KEY `gz_id` (`gz_id`),
- CONSTRAINT `gz_ibfk_1` FOREIGN KEY (`gz_id`) REFERENCES `yg` (`yg_id`) ON DELETE CASCADE ON UPDATE CASCADE
- ) ENGINE=InnoDB DEFAULT CHARSET=utf8
- 1 row in set (0.00 sec)
其中gz_ibfk_1即删除外键约束时要用到的名称。
删除操作:
- mysql> ALTER TABLE gz DROP FOREIGN KEY gz_ibfk_1;
- Query OK, 0 rows affected (0.01 sec)
- Records: 0 Duplicates: 0 Warnings: 0
确认删除结果:
- mysql> SHOW CREATE TABLE gz\G
- *************************** 1. row ***************************
- Table: gz
- Create Table: CREATE TABLE `gz` (
- `gz_id` int(4) NOT NULL,
- `name` char(16) NOT NULL,
- `gz` float(7,2) NOT NULL DEFAULT ‘0.00‘,
- KEY `name` (`name`),
- KEY `gz_id` (`gz_id`)
- ) ENGINE=InnoDB DEFAULT CHARSET=utf8
- 1 row in set (0.00 sec)
2 MySQL存储引擎的配置
2.1 问题
本案例要求MySQL数据存储引擎的使用,完成以下任务操作:
- 可用的存储引擎类型
- 查看默认存储类型
- 更改表的存储引擎
2.2 步骤
实现此案例需要按照如下步骤进行。
步骤一:查看存储引擎信息
登入MySQL服务器,查看当前支持哪些存储引擎。
使用mysql命令连接,以root用户登入:
- [[email protected] ~]# mysql -u root –p
- Enter password:
- Welcome to the MySQL monitor. Commands end with ; or \g.
- Your MySQL connection id is 9
- Server version: 5.7.17 MySQL Community Server (GPL)
- Copyright (c) 2000, 2016, Oracle and/or its affiliates. All rights reserved.
- Oracle is a registered trademark of Oracle Corporation and/or its
- affiliates. Other names may be trademarks of their respective
- owners.
- Type ‘help;‘ or ‘\h‘ for help. Type ‘\c‘ to clear the current input statement.
- mysql>
执行SHOW ENGINES\G指令可列表查看,MySQL 5.6可用的存储引擎有9种(除最后的FEDERATED以外,其他8种都支持),其中默认采用的存储引擎为InnoDB:
- mysql> SHOW ENGINES\G
- *************************** 1. row ***************************
- Engine: InnoDB
- Support: DEFAULT //此存储引擎为默认
- Comment: Supports transactions, row-level locking, and foreign keys
- Transactions: YES
- XA: YES
- Savepoints: YES
- *************************** 2. row ***************************
- Engine: MRG_MYISAM
- Support: YES
- Comment: Collection of identical MyISAM tables
- Transactions: NO
- XA: NO
- Savepoints: NO
- *************************** 3. row ***************************
- Engine: MEMORY
- Support: YES
- Comment: Hash based, stored in memory, useful for temporary tables
- Transactions: NO
- XA: NO
- Savepoints: NO
- *************************** 4. row ***************************
- Engine: BLACKHOLE
- Support: YES
- Comment: /dev/null storage engine (anything you write to it disappears)
- Transactions: NO
- XA: NO
- Savepoints: NO
- *************************** 5. row ***************************
- Engine: MyISAM
- Support: YES
- Comment: MyISAM storage engine
- Transactions: NO
- XA: NO
- Savepoints: NO
- *************************** 6. row ***************************
- Engine: CSV
- Support: YES
- Comment: CSV storage engine
- Transactions: NO
- XA: NO
- Savepoints: NO
- *************************** 7. row ***************************
- Engine: ARCHIVE
- Support: YES
- Comment: Archive storage engine
- Transactions: NO
- XA: NO
- Savepoints: NO
- *************************** 8. row ***************************
- Engine: PERFORMANCE_SCHEMA
- Support: YES
- Comment: Performance Schema
- Transactions: NO
- XA: NO
- Savepoints: NO
- *************************** 9. row ***************************
- Engine: FEDERATED
- Support: NO //此引擎不被支持
- Comment: Federated MySQL storage engine
- Transactions: NULL
- XA: NULL
- Savepoints: NULL
- 9 rows in set (0.01 sec)
或者直接查看系统变量default_storage_engine 的值,也可确认默认采用的存储引擎是InnoDB:
- mysql> SHOW VARIABLES LIKE ‘default_storage_engine‘;
- +------------------------+--------+
- | Variable_name | Value |
- +------------------------+--------+
- | default_storage_engine | InnoDB |
- +------------------------+--------+
- 1 row in set (0.00 sec)
步骤二:修改默认存储引擎
在 mysql> 环境中,可以直接通过SET指令更改默认的存储引擎(只在本次连接会话过程中有效,退出重进即失效) 。比如临时修改为MyISAM,可执行下列操作:
- mysql> SET default_storage_engine=MyISAM; //改用MyISAM引擎
- Query OK, 0 rows affected (0.00 sec)
- mysql> SHOW VARIABLES LIKE ‘default_storage_engine‘; //确认结果
- +------------------------+--------+
- | Variable_name | Value |
- +------------------------+--------+
- | default_storage_engine | MyISAM |
- +------------------------+--------+
- 1 row in set (0.00 sec)
若希望直接修改MySQL服务程序所采用的默认存储引擎,应将相关设置写入配置文件/etc/my.cnf,并重启服务后生效。比如:
- [[email protected] ~]# vim /etc/my.cnf
- [mysqld]
- .. ..
- default_storage_engine=MEMORY //改用MEMORY引擎
- [[email protected] ~]# systemctl restart mysqld.service //重启服务
重新登入 mysql> 确认修改结果:
- [[email protected] ~]# mysql -u root -p
- Enter password:
- Welcome to the MySQL monitor. Commands end with ; or \g.
- Your MySQL connection id is 3
- Server version: 5.7.17 MySQL Community Server (GPL)
- Copyright (c) 2000, 2016, Oracle and/or its affiliates. All rights reserved.
- Oracle is a registered trademark of Oracle Corporation and/or its
- affiliates. Other names may be trademarks of their respective
- owners.
- Type ‘help;‘ or ‘\h‘ for help. Type ‘\c‘ to clear the current input statement.
- mysql> SHOW VARIABLES LIKE ‘default_storage_engine‘;
- +------------------------+--------+
- | Variable_name | Value |
- +------------------------+--------+
- | default_storage_engine | MEMORY | //默认引擎已修改
- +------------------------+--------+
- 1 row in set (0.00 sec)
- mysql> exit
- Bye
为了避免后续实验障碍,测试完后记得恢复原状——移除默认引擎设置,或者将其修改为InnoDB即可:
- [[email protected] ~]# vim /etc/my.cnf
- [mysqld]
- .. ..
- default_storage_engine=InnoDB
- [[email protected] ~]# systemctl restart mysqld.service
确认恢复结果(选项 -e 可调用指定的SQL操作后返回Shell命令行):
- [[email protected] ~]# mysql -u root -p -e "SHOW VARIABLES LIKE ‘default_storage_engine‘;"
- Enter password:
- +------------------------+--------+
- | Variable_name | Value |
- +------------------------+--------+
- | default_storage_engine | InnoDB |
- +------------------------+--------+
原文地址:https://www.cnblogs.com/xiaoren112/p/8318692.html