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NSD DBA1 DAY02

  1. 修改表结构
  2. MySQL索引创建与删除

1 修改表结构

1.1 问题

本案例要求熟悉MySQL库中表的字段修改,主要练习以下操作:

1.2 步骤

实现此案例需要按照如下步骤进行。

步骤一:添加字段

在studb中创建tea6表

  1. mysql> CREATE TABLE studb.tea6(id int(4) PRIMARY KEY,
  2. -> name varchar(4) NOT NULL,
  3. -> age int(2) NOT NULL
  4. -> );
  5. Query OK, 0 rows affected (0.34 sec)

为tea6表添加一个address字段

添加前:

  1. mysql> DESC tea6;
  2. +-------+------------+------+-----+---------+-------+
  3. | Field | Type | Null | Key | Default | Extra |
  4. +-------+------------+------+-----+---------+-------+
  5. | id | int(4) | NO | PRI | NULL | |
  6. | name | varchar(4) | NO | | NULL | |
  7. | age | int(2) | NO | | NULL | |
  8. +-------+------------+------+-----+---------+-------+
  9. 3 rows in set (0.00 sec)

添加address字段:

  1. mysql> ALTER TABLE tea6 ADD address varchar(48);
  2. Query OK, 0 rows affected (0.84 sec)
  3. Records: 0 Duplicates: 0 Warnings: 0

添加后(默认作为最后一个字段):

  1. mysql> DESC tea6;
  2. +---------+-------------+------+-----+---------+-------+
  3. | Field | Type | Null | Key | Default | Extra |
  4. +---------+-------------+------+-----+---------+-------+
  5. | id | int(4) | NO | PRI | NULL | |
  6. | name | varchar(4) | NO | | NULL | |
  7. | age | int(2) | NO | | NULL | |
  8. | address | varchar(48) | YES | | NULL | |
  9. +---------+-------------+------+-----+---------+-------+
  10. 4 rows in set (0.00 sec)

3)在tea6表的age列之后添加一个gender字段

添加操作:

  1. mysql> ALTER TABLE tea6 ADD gender enum('boy','girl') AFTER age;
  2. Query OK, 0 rows affected (0.59 sec)
  3. Records: 0 Duplicates: 0 Warnings: 0

确认添加结果:

  1. mysql> DESC tea6;
  2. +---------+--------------------+------+-----+---------+-------+
  3. | Field | Type | Null | Key | Default | Extra |
  4. +---------+--------------------+------+-----+---------+-------+
  5. | id | int(4) | NO | PRI | NULL | |
  6. | name | varchar(4) | NO | | NULL | |
  7. | age | int(2) | NO | | NULL | |
  8. | gender | enum('boy','girl') | YES | | NULL | |
  9. | address | varchar(48) | YES | | NULL | |
  10. +---------+--------------------+------+-----+---------+-------+
  11. 5 rows in set (0.00 sec)

步骤二:修改字段名和字段类型

将tea6表的gender字段改名为sex,并添加非空约束

修改操作:

  1. mysql> ALTER TABLE tea6 CHANGE gender
  2. -> sex enum('boy','girl') NOT NULL;
  3. Query OK, 0 rows affected (0.08 sec)
  4. Records: 0 Duplicates: 0 Warnings: 0

确认修改结果:

  1. mysql> DESC tea6;
  2. +---------+--------------------+------+-----+---------+-------+
  3. | Field | Type | Null | Key | Default | Extra |
  4. +---------+--------------------+------+-----+---------+-------+
  5. | id | int(4) | NO | PRI | NULL | |
  6. | name | varchar(4) | NO | | NULL | |
  7. | age | int(2) | NO | | NULL | |
  8. | sex | enum('boy','girl') | NO | | NULL | |
  9. | address | varchar(48) | YES | | NULL | |
  10. +---------+--------------------+------+-----+---------+-------+
  11. 5 rows in set (0.00 sec)

步骤三:删除字段

删除tea6表中名为sex的字段:

  1. mysql> ALTER TABLE tea6 DROP sex; //删除操作
  2. Query OK, 0 rows affected (0.52 sec)
  3. Records: 0 Duplicates: 0 Warnings: 0
  4.  
  5. mysql> DESC tea6;                                         //确认删除结果
  6. +---------+-------------+------+-----+---------+-------+
  7. | Field | Type | Null | Key | Default | Extra |
  8. +---------+-------------+------+-----+---------+-------+
  9. | id | int(4) | NO | PRI | NULL | |
  10. | name | varchar(4) | NO | | NULL | |
  11. | age | int(2) | NO | | NULL | |
  12. | address | varchar(48) | YES | | NULL | |
  13. +---------+-------------+------+-----+---------+-------+
  14. 4 rows in set (0.00 sec)

2 MySQL索引创建与删除

2.1 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:

表-1 员工表yg的数据

表-2 工资表gz的数据

2.2 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:

  1. mysql> create database home;
  2. 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:

  1. mysql> USE home;
  2. Database changed
  3. mysql> CREATE TABLE tea4(
  4. -> id char(6) NOT NULL,
  5. -> name varchar(6) NOT NULL,
  6. -> age int(3) NOT NULL,
  7. -> gender ENUM('boy','girl') DEFAULT 'boy',
  8. -> INDEX(id),INDEX(name)
  9. -> );
  10. 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:

  1. mysql> DESC tea4;
  2. +--------+--------------------+------+-----+---------+-------+
  3. | Field | Type | Null | Key | Default | Extra |
  4. +--------+--------------------+------+-----+---------+-------+
  5. | id | char(6) | NO | MUL | NULL | |
  6. | name | varchar(6) | NO | MUL | NULL | |
  7. | age | int(3) | NO | | NULL | |
  8. | gender | enum('boy','girl') | YES | | boy | |
  9. +--------+--------------------+------+-----+---------+-------+
  10. 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:

  1. mysql> drop INDEX name ON tea4; //删除name字段的索引
  2. Query OK, 0 rows affected (0.18 sec)
  3. Records: 0 Duplicates: 0 Warnings: 0
  4.  
  5. mysql> DESC tea4; //确认删除结果
  6. +--------+--------------------+------+-----+---------+-------+
  7. | Field | Type | Null | Key | Default | Extra |
  8. +--------+--------------------+------+-----+---------+-------+
  9. | id | char(6) | NO | MUL | NULL | |
  10. | name | varchar(6) | NO | | NULL | |
  11. | age | int(3) | NO | | NULL | |
  12. | gender | enum('boy','girl') | YES | | boy | |
  13. +--------+--------------------+------+-----+---------+-------+
  14. 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:

  1. mysql> CREATE INDEX nianling ON tea4(age);     //针对指定字段创建索引
  2. Query OK, 0 rows affected (0.62 sec)
  3. Records: 0 Duplicates: 0 Warnings: 0
  4.  
  5. mysql> DESC tea4;                                 //确认创建结果
  6. +--------+--------------------+------+-----+---------+-------+
  7. | Field | Type | Null | Key | Default | Extra |
  8. +--------+--------------------+------+-----+---------+-------+
  9. | id | char(6) | NO | MUL | NULL | |
  10. | name | varchar(6) | NO | | NULL | |
  11. | age | int(3) | NO | MUL | NULL | |
  12. | gender | enum('boy','girl') | YES | | boy | |
  13. +--------+--------------------+------+-----+---------+-------+
  14. 4 rows in set (0.00 sec)

4)查看指定表的索引信息

使用SHOW INDEX 指令:

  1. mysql> SHOW INDEX FROM tea4\G
  2. *************************** 1. row ***************************
  3. Table: tea4
  4. Non_unique: 1
  5. Key_name: id
  6. Seq_in_index: 1
  7. Column_name: id
  8. Collation: A
  9. Cardinality: 0
  10. Sub_part: NULL
  11. Packed: NULL
  12. Null:
  13. Index_type: BTREE //使用B树算法
  14. Comment:
  15. Index_comment:
  16. *************************** 2. row ***************************
  17. Table: tea4
  18. Non_unique: 1
  19. Key_name: nianling //索引名称
  20. Seq_in_index: 1
  21. Column_name: age //字段名称
  22. Collation: A
  23. Cardinality: 0
  24. Sub_part: NULL
  25. Packed: NULL
  26. Null:
  27. Index_type: BTREE
  28. Comment:
  29. Index_comment:
  30. 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:

  1. mysql> CREATE TABLE tea5(
  2. -> id char(6),
  3. -> name varchar(4) NOT NULL,
  4. -> age int(3) NOT NULL,
  5. -> UNIQUE(id),UNIQUE(name),INDEX(age)
  6. -> );
  7. 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:

  1. mysql> DESC tea5;                                     //确认设置结果
  2. +-------+------------+------+-----+---------+-------+
  3. | Field | Type | Null | Key | Default | Extra |
  4. +-------+------------+------+-----+---------+-------+
  5. | id | char(6) | YES | UNI | NULL | |
  6. | name | varchar(4) | NO | PRI | NULL | |
  7. | age | int(3) | NO | MUL | NULL | |
  8. +-------+------------+------+-----+---------+-------+
  9. 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):

  1. mysql> DROP INDEX name ON tea5;                     //清除UNIQUE索引
  2. Query OK, 0 rows affected (0.97 sec)
  3. Records: 0 Duplicates: 0 Warnings: 0
  4.  
  5. mysql> DESC tea5;                                     //确认删除结果
  6. +-------+------------+------+-----+---------+-------+
  7. | Field | Type | Null | Key | Default | Extra |
  8. +-------+------------+------+-----+---------+-------+
  9. | id | char(6) | YES | UNI | NULL | |
  10. | name | varchar(4) | NO | | NULL | |
  11. | age | int(3) | NO | MUL | NULL | |
  12. +-------+------------+------+-----+---------+-------+
  13. 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:

  1. mysql> CREATE UNIQUE INDEX name ON tea5(name);     //建立UNIQUE索引
  2. Query OK, 0 rows affected (0.47 sec)
  3. Records: 0 Duplicates: 0 Warnings: 0
  4.  
  5. mysql> DESC tea5;                                     //确认设置结果
  6. +-------+------------+------+-----+---------+-------+
  7. | Field | Type | Null | Key | Default | Extra |
  8. +-------+------------+------+-----+---------+-------+
  9. | id | char(6) | YES | UNI | NULL | |
  10. | name | varchar(4) | NO | PRI | NULL | |
  11. | age | int(3) | NO | MUL | NULL | |
  12. +-------+------------+------+-----+---------+-------+
  13. 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:

  1. mysql> CREATE TABLE biao01(
  2. -> id int(4) PRIMARY KEY,                     //直接在字段定义时约束
  3. -> name varchar(8)
  4. -> );
  5. Query OK, 0 rows affected (0.19 sec)

或者:

  1. mysql> CREATE TABLE biao02(
  2. -> id int(4),
  3. -> name varchar(8),
  4. -> PRIMARY KEY(id)                             //所有字段定义完,最后指定
  5. -> );
  6. 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:

  1. mysql> CREATE TABLE tea6(
  2. -> id int(4) AUTO_INCREMENT,
  3. -> name varchar(4) NOT NULL,
  4. -> age int(2) NOT NULL,
  5. -> PRIMARY KEY(id)
  6. -> );
  7. 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):

  1. mysql> DESC biao01;
  2. +-------+------------+------+-----+---------+-------+
  3. | Field | Type | Null | Key | Default | Extra |
  4. +-------+------------+------+-----+---------+-------+
  5. | id | int(4) | NO | PRI | NULL | |
  6. | name | varchar(8) | YES | | NULL | |
  7. +-------+------------+------+-----+---------+-------+
  8. 2 rows in set (0.00 sec)

清除操作:

  1. mysql> ALTER TABLE biao01 DROP PRIMARY KEY;
  2. Query OK, 0 rows affected (0.49 sec)
  3. Records: 0 Duplicates: 0 Warnings: 0

清除后(无主键):

  1. mysql> DESC biao01;
  2. +-------+------------+------+-----+---------+-------+
  3. | Field | Type | Null | Key | Default | Extra |
  4. +-------+------------+------+-----+---------+-------+
  5. | id | int(4) | NO | | NULL | |
  6. | name | varchar(8) | YES | | NULL | |
  7. +-------+------------+------+-----+---------+-------+
  8. 2 rows in set (0.00 sec)

当尝试删除tea6表的主键时,会出现异常:

  1. mysql> ALTER TABLE tea6 DROP PRIMARY KEY;
  2. 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:

  1. mysql> ALTER TABLE tea6 MODIFY id int(4) NOT NULL;
  2. Query OK, 0 rows affected (0.75 sec)
  3. Records: 0 Duplicates: 0 Warnings: 0

然后再清除主键属性就OK了:

  1. mysql> ALTER TABLE tea6 DROP PRIMARY KEY;                 //清除主键
  2. Query OK, 0 rows affected (0.39 sec)
  3. Records: 0 Duplicates: 0 Warnings: 0
  4.  
  5. mysql> desc tea6; //确认清除结果
  6. +-------+------------+------+-----+---------+-------+
  7. | Field | Type | Null | Key | Default | Extra |
  8. +-------+------------+------+-----+---------+-------+
  9. | id | int(4) | NO | | NULL | |
  10. | name | varchar(4) | NO | | NULL | |
  11. | age | int(2) | NO | | NULL | |
  12. +-------+------------+------+-----+---------+-------+
  13. 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:

  1. mysql> ALTER TABLE tea6 ADD PRIMARY KEY(id);             //设置主键字段
  2. Query OK, 0 rows affected (0.35 sec)
  3. Records: 0 Duplicates: 0 Warnings: 0
  4.  
  5. mysql> DESC tea6;                                         //确认设置结果
  6. +-------+------------+------+-----+---------+-------+
  7. | Field | Type | Null | Key | Default | Extra |
  8. +-------+------------+------+-----+---------+-------+
  9. | id | int(4) | NO | PRI | NULL | |
  10. | name | varchar(4) | NO | | NULL | |
  11. | age | int(2) | NO | | NULL | |
  12. +-------+------------+------+-----+---------+-------+
  13. 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

  1. mysql> CREATE TABLE yg(
  2. -> yg_id int(4) AUTO_INCREMENT,
  3. -> name char(16) NOT NULL,
  4. -> PRIMARY KEY(yg_id)
  5. -> );
  6. 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:

  1. mysql> CREATE TABLE gz(
  2. -> gz_id int(4) NOT NULL,
  3. -> name char(16) NOT NULL,
  4. -> gz float(7,2) NOT NULL DEFAULT 0,
  5. -> INDEX(name),
  6. -> FOREIGN KEY(gz_id) REFERENCES yg(yg_id)
  7. -> ON UPDATE CASCADE ON DELETE CASCADE
  8. -> );
  9. 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:

  1. mysql> INSERT INTO yg(name) VALUES('Jerry'),('Tom');
  2. Query OK, 2 rows affected (0.16 sec)
  3. Records: 2 Duplicates: 0 Warnings: 0

确认yg表的数据记录:

  1. mysql> SELECT * FROM yg;
  2. +-------+-------+
  3. | yg_id | name |
  4. +-------+-------+
  5. | 1 | Jerry |
  6. | 2 | Tom |
  7. +-------+-------+
  8. 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):

  1. mysql> INSERT INTO gz(gz_id,name,gz)
  2. -> VALUES(1,'Jerry',12000),(2,'Tom',8000)
  3. -> ;
  4. Query OK, 2 rows affected (0.06 sec)
  5. Records: 2 Duplicates: 0 Warnings: 0

确认gz表的数据记录:

  1. mysql> SELECT * FROM gz;
  2. +-------+-------+----------+
  3. | gz_id | name | gz |
  4. +-------+-------+----------+
  5. | 1 | Jerry | 12000.00 |
  6. | 2 | Tom | 8000.00 |
  7. +-------+-------+----------+
  8. 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:

  1. mysql> update yg SET yg_id=1234 WHERE name='Jerry';
  2. Query OK, 1 row affected (0.05 sec)
  3. Rows matched: 1 Changed: 1 Warnings: 0

确认修改结果:

  1. mysql> SELECT * FROM yg;
  2. +-------+-------+
  3. | yg_id | name |
  4. +-------+-------+
  5. | 2 | Tom |
  6. | 1234 | Jerry |
  7. +-------+-------+
  8. 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:

  1. mysql> SELECT * FROM gz;
  2. +-------+-------+----------+
  3. | gz_id | name | gz |
  4. +-------+-------+----------+
  5. | 1234 | Jerry | 12000.00 |
  6. | 2 | Tom | 8000.00 |
  7. +-------+-------+----------+
  8. 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:

  1. mysql> DELETE FROM yg WHERE name='Jerry';
  2. Query OK, 1 row affected (0.05 sec)

确认删除结果:

  1. mysql> SELECT * FROM yg;
  2. +-------+------+
  3. | yg_id | name |
  4. +-------+------+
  5. | 2 | Tom |
  6. +-------+------+
  7. 1 row in set (0.00 sec)

查看gz表中的变化(Jerry的记录也没了):

  1. mysql> SELECT * FROM gz;
  2. +-------+------+---------+
  3. | gz_id | name | gz |
  4. +-------+------+---------+
  5. | 2 | Tom | 8000.00 |
  6. +-------+------+---------+
  7. 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:

  1. mysql> SHOW CREATE TABLE gz\G
  2. *************************** 1. row ***************************
  3. Table: gz
  4. Create Table: CREATE TABLE `gz` (
  5. `gz_id` int(4) NOT NULL,
  6. `name` char(16) NOT NULL,
  7. `gz` float(7,2) NOT NULL DEFAULT '0.00',
  8. KEY `name` (`name`),
  9. KEY `gz_id` (`gz_id`),
  10. CONSTRAINT `gz_ibfk_1` FOREIGN KEY (`gz_id`) REFERENCES `yg` (`yg_id`) ON DELETE CASCADE ON UPDATE CASCADE
  11. ) ENGINE=InnoDB DEFAULT CHARSET=utf8
  12. 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:

  1. mysql> ALTER TABLE gz DROP FOREIGN KEY gz_ibfk_1;
  2. Query OK, 0 rows affected (0.01 sec)
  3. Records: 0 Duplicates: 0 Warnings: 0

确认删除结果:

  1. mysql> SHOW CREATE TABLE gz\G
  2. *************************** 1. row ***************************
  3. Table: gz
  4. Create Table: CREATE TABLE `gz` (
  5. `gz_id` int(4) NOT NULL,
  6. `name` char(16) NOT NULL,
  7. `gz` float(7,2) NOT NULL DEFAULT '0.00',
  8. KEY `name` (`name`),
  9. KEY `gz_id` (`gz_id`)
  10. ) ENGINE=InnoDB DEFAULT CHARSET=utf8
  11. 1 row in set (0.00 sec)