MariaDB数据库（二）

+--------------------+ | Database | +--------------------+ | information_schema | | mysql | | performance_schema | | testbase | +--------------------+

　　创建数据库testdb用作实验

MariaDB [(none)]> create database testdb character set utf8;    #支持中文
MariaDB [(none)]> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| testdb             |
+--------------------+

　　使用数据库testdb

MariaDB [(none)]> use testdb;
MariaDB [testdb]> show tables;                        #查看表
Empty set (0.000 sec)                                 #空表

　　创建一个classes表，有ip、name两个字段（列），ip为无符号的整型数，设置有主键，name为VARCHAR类型的字符串

MariaDB [testdb]> create table classes (id tinyint unsigned primary key,name varchar(20));
Query OK, 0 rows affected (0.005 sec)
MariaDB [testdb]> show tables;
+-------------------+
| Tables_in_testdb  |
+-------------------+
| classes           |
+-------------------+

　　查看表的字段

MariaDB [testdb]> desc classes;    #describe，描述
+-------+---------------------+------+-----+---------+------+
| Field | Type                | Null | Key | Default | Extra|
+-------+---------------------+------+-----+---------+------+
| id    | tinyint(3) unsigned | NO   | PRI | NULL    |      |
| name  | varchar(20)         | YES  |     | NULL    |      |
+-------+---------------------+------+-----+---------+------+
 #定义     类型                是否为空 是否主键  默认值    扩展

　　linux当中的注释用#，而数据库中的注释用--

　　创建一个复杂的students表，包含字段id、name、age、high、gender、cls_id

MariaDB [testdb]> create table students (id tinyint unsigned primary key auto_increment,
    -> name varchar(20),        
    -> age tinyint unsigned,
　　-> gender enum(‘男‘, ‘女‘, ‘人妖‘,‘保密‘)not null default ‘人妖‘,   #枚举，默认为‘人妖’
    -> cls_id tinyint unsigned
　　-> );
MariaDB [testdb]> show tables;
+------------------+
| Tables_in_testdb |
+------------------+
| classes          |
| students         |
+------------------+
MariaDB [testdb]> desc students;
+--------+-----------------------------+------+-----+----------+---------------+
| Field  | Type                        | Null | Key | Default | Extra          |
+--------+-----------------------------+------+-----+---------+----------------+
| id     | tinyint(3) unsigned         | NO   | PRI | NULL    | auto_increment |
| name  | varchar(20)                  | YES  |     | NULL    |                |
| age   | tinyint(3) unsigned          | YES  |     | NULL    |                |
| gender | enum(‘男‘,‘女‘,‘人妖‘,‘保密‘) | NO   |     | 人妖    |                |
| cls_id | tinyint(3) unsigned         | YES  |     | NULL    |                |
+--------+-----------------------------+------+-----+---------+----------------+

　　查看表的创建

MariaDB [testdb]> show create table students;
……..                                                  #列出语法
| students | CREATE TABLE `students` (
  `id` tinyint(3) unsigned NOT NULL AUTO_INCREMENT,
  `name` varchar(20) DEFAULT NULL,
  `age` tinyint(3) unsigned DEFAULT NULL,
  `gender` enum(‘男‘,‘女‘,‘人妖‘,‘保密‘) NOT NULL DEFAULT ‘人妖‘,
  `cls_id` tinyint(3) unsigned DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8                  #默认引擎为InnoDB
………

MariaDB处理引擎有InnoDB、MyISAM、blackhole等，最主要的区别在于InnoDB支持事务处理与外键和行级锁。

2> 改字段

　　修改表：修改用命令alter

　　添加一个brithday字段，类型为date

MariaDB [testdb]> alter table students add brithday date;
MariaDB [testdb]> desc students;
+----------+--------------------------------------+-----+---------+----------------+
| Field    | Type                          | Null | Key | Default | Extra          |
+----------+--------------------------------------+-----+---------+----------------+
| id       | tinyint(3) unsigned           | NO   | PRI | NULL    | auto_increment |
| name     | varchar(20)                   | YES  |     | NULL    |                |
| age      | tinyint(3) unsigned           | YES  |     | NULL    |                |
| gender   | enum(‘男‘,‘女‘,‘人妖‘,‘保密‘)   | NO   |人妖 |         |                |
| cls_id   | tinyint(3) unsigned    YES    |      |NULL |         |                |
| brithday | date                          | YES  |     | NULL    |                |

　　更改字段名

MariaDB [testdb]> alter table students change brithday birthday date;

　　更改表的类型

MariaDB [testdb]> alter table students modify birthday datetime;

　　删除字段

MariaDB [testdb]> alter table students drop birthday;

　　删除表

MariaDB [testdb]> drop table students;

 

3>  给字段插入数据

　　向students表插入数据，value接值，ip为1，name为zxj，字符串类型用单引号引起，age为250，high为250.253，gender为人妖id_cls为1

MariaDB [testdb]> insert into students values (1,‘zxj‘,250.253,‘人妖‘,1);

　　查看插入的字段

MariaDB [testdb]> select * from students;
+----+------+------+--------+--------+
| id | name | age  | gender | cls_id |
+----+------+------+--------+--------+
|  1 | zxj  | 250  | 人妖    |    1   |
+----+------+------+--------+--------+
1 row in set (0.000 sec)

　　由于id设置的是自增，因此每次插入时id都是增加的，为体现效果，手动插入id为4的一条数据

MariaDB [testdb]> select * from students;
+----+------+------+--------+--------+
| id | name | age  | gender | cls_id |
+----+------+------+--------+--------+
|  1 | zxj  |  250 | 人妖    |    1   |
|  4 | zxj  |  250 | 人妖    |    1   |
+----+------+------+--------+--------+

MariaDB [testdb]> insert into students values (0,‘zxj‘,250.253,‘人妖‘,1);
Query OK, 1 row affected (0.001 sec)

MariaDB [testdb]> select * from students;
+----+------+------+--------+--------+
| id | name | age  | gender | cls_id |
+----+------+------+--------+--------+
|  1 | zxj  |  250 | 人妖    |    1   |
|  4 | zxj  |  250 | 人妖    |    1   |
|  5 | zxj  |  250 | 人妖    |    1   |
+----+------+------+--------+--------+
3 rows in set (0.000 sec)

MariaDB [testdb]> show create table students;
….
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8       #当前默认值为为6，因此下一次默认添加数据时自增为6

　　对部分插入，比如仅对name、age添加数据

MariaDB [testdb]> insert into students (name,age) values (‘wrl‘ ,24);
MariaDB [testdb]> select * from students;
+----+------+------+--------+--------+
| id | name | age  | gender | cls_id |
+----+------+------+--------+--------+
|  1 | zxj  |  250 | 人妖   |    1   |
|  4 | zxj  |  250 | 人妖   |    1   |
|  5 | zxj  |  250 | 人妖   |    1   |
|  6 | wrl  |   24 | 人妖   |  NULL  |                        #gender设置了默认值为‘人妖’
+----+------+------+-------+---------+

　　删除一条数据

MariaDB [testdb]> delete from students where id=6;           #条件表达式where
MariaDB [testdb]> select * from students;
+----+------+------+--------+--------+
| id | name | age  | gender | cls_id |
+----+------+------+--------+--------+
|  1 | zxj  |  250 | 人妖    |     1  |
|  4 | zxj  |  250 | 人妖    |     1  |
|  5 | zxj  |  250 | 人妖    |     1  |
+----+------+------+--------+--------+

　　插入多条数据

MariaDB [testdb]> insert into students (name,age) values (‘wrl‘ ,24),(‘my‘,23);   #多条数据以逗号隔开，字符串加单引号
MariaDB [testdb]> select * from students;
+----+------+------+--------+--------+
| id | name | age  | gender | cls_id |
+----+------+------+--------+--------+
|  1 | zxj  |  250 | 人妖   |      1 |
|  4 | zxj  |  250 | 人妖   |      1 |
|  5 | zxj  |  250 | 人妖   |      1 |
|  7 | wrl  |   24 | 人妖   |  NULL  |
|  8 | my   |   23 | 人妖   |  NULL  |

4> 修改字段数据，用命令update

　　修改id>=7的数据的gender为‘保密’

MariaDB [testdb]> update students set gender=‘保密‘ where id>=7;
MariaDB [testdb]> select * from students;
+----+------+------+----------+-------+
| id | name | age  |  gender  |cls_id |
+----+------+------+--------- +-------+
|  1 | zxj  |  250 |   人妖   |      1 |
|  4 | zxj  |  250 |   人妖   |      1 |
|  5 | zxj  |  250 |   人妖   |      1 |
|  7 | wrl  |   24 |   保密   |  NULL  |
|  8 | my   |   23 |   保密   |  NULL  |
+----+------+------+---------+--------+

　　由于gender设置是枚举，选项有四个，因此可以用1、2、3、4来代替男、女、人妖、保密 四个选项。

MariaDB [testdb]> update students set gender=1 where id=7;
MariaDB [testdb]> update students set gender=2 where id=8;
MariaDB [testdb]> update students set gender=4 where name=‘zxj‘;
MariaDB [testdb]> select * from  students;
+----+------+------+---------+----------+
| id | name | age  | gender  | cls_id   |
+----+------+------+---------+----------+
|  1 | zxj  |  250 |  保密   |         1 |
|  4 | zxj  |  250 |  保密   |         1 |
|  5 | zxj  |  250 |  保密   |         1 |
|  7 | wrl  |   24 |  男     |      NULL |
|  8 | my   |   23 |  女     |      NULL |
+----+------+------+--------+-----------+

　　还可以修改多条数据的多个字段（列），如

MariaDB [testdb]> update students set gender=2,age=23 where name=‘zxj‘;
Query OK, 3 rows affected (0.001 sec)
Rows matched: 3  Changed: 3  Warnings: 0
MariaDB [testdb]> select * from students;
+----+------+------+--------+--------+
| id | name | age  | gender | cls_id |
+----+------+------+--------+--------+
|  1 | zxj  |   23 | 女     |    1   |
|  4 | zxj  |   23 | 女     |    1   |
|  5 | zxj  |   23 | 女     |    1   |
|  7 | wrl  |   24 | 男     |NULL    |
|  8 | my   |   23 | 女     |NULL    |
+----+------+------+--------+--------+
5 rows in set (0.000 sec)

 

5> 删除

　　删除students表中id为4、5的数据

MariaDB [testdb]> delete from students where id=4;
MariaDB [testdb]> delete from students where id=5;
MariaDB [testdb]> select * from students;
+----+------+------+--------+--------+
| id | name | age  | gender | cls_id |
+----+------+------+--------+--------+
|  1 | zxj  |  23  | 女     |     1  |
|  7 | wrl  |  24  | 男     | NULL   |
|  8 | my   |  23  | 女     | NULL   |
+----+------+------+--------+--------+

　　清空表。清空表的内容不要随便用，会清除所有数据。

MariaDB [testdb]> delete from students;

 

面试：用delete并不会清除自增AUTO_UNCREMENT的值，若要清空表后重置自增值为1，用truncate命令，truncate会清空表的所有内容且不可恢复（不能回滚）。

MariaDB [testdb]> truncate table students；

 

6> 逻辑删除　

　　用一条字段来表示这条信息是否已经不能在使用了，比如游戏企业通过设置一个字段来表示哪些用户活跃，哪些用户不活跃等。一般企业都将逻辑删除标记为bit（0和1）。逻辑删除并不会删除磁盘数据。

　　先在students表中添加一个逻辑删除标记ls_delete，bit类型，默认为0

MariaDB [testdb]> alter table students add is_delete  bit default 0;
MariaDB [testdb]> desc students;
………
| is_delete | bit(1)                              | YES  |     | b‘0‘    |               
MariaDB [testdb]> insert into students (name,age,is_delete) values (‘jony‘,24,1);
MariaDB [testdb]> select * from students;
+----+------+------+--------+--------+-----------+
| id | name | age  | gender | cls_id | is_delete |
+----+------+------+--------+--------+-----------+
|  1 | zxj  |   23 | 女     |      1 |           |        #bit=0数值较小，不显示不代表没有
|  7 | wrl  |   24 | 男     |   NULL |           ||  8 | my   |   23 | 女     |   NULL |           |
|  9 | jony |   24 | 人妖   |   NULL | 口         |        #bit=1
+----+------+------+--------+--------+-----------+
4 rows in set (0.000 sec)

　　用is_delete来表明删除项，如筛选bit不为0的用户

MariaDB [testdb]> select * from students where is_delete=0;
+----+------+------+--------+--------+-----------+
| id | name | age  | gender | cls_id | is_delete |
+----+------+------+--------+--------+-----------+
|  1 | zxj  |  23  | 女     |     1  |           |
|  7 | wrl  |  24  | 男     | NULL   |           |
|  8 | my   |  23  | 女     | NULL   |           |
+----+------+------+--------+--------+-----------+

MariaDB数据库（二）

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