MySQL ?學習筆記

一.安裝

Typical:經典安裝

Custom:自定義安裝

Complete: 完全安裝

二.修改編碼方式

[mysqld]

myini:character-set-server=utf8

[client] port=3306 default-character-set=utf8

三.啟動停止mysql服務

cmd net stop mysql

cmd net start mysql

四.MySQL登錄

mysql -V 查看版本，并退出

mysql -uroot -p -P3306 -h127.0.0.1 登錄本地mysql

mysql>exit; 退出

mysql>quit; 退出

mysql>\q; 退出

五.修改MySQL提示符

shell>mysql -uroot -proot --prompt 新提示符 \h localhost

mysql>prompt 新提示符

(\D 完整日期 ?\d 當前數據庫 \h 服務器名稱 ?\u當前用戶)

六.常用命令&語句規范

select version() 顯示服務器版本

select now() 顯示當前日期時間

select user() 顯示當前用戶

關鍵字與函數名全部大寫

數據庫名稱，表名稱，字段名稱全部小寫

SQL語句以分號結尾

七.操作數據庫

創建數據庫

create {database|schema} ?[if not exist] db_name [default] character set [=] charset_name

create database t1;

create database if not exists t2 character set utf8;

查看數據

show {databases|schemas} [like 'pattern' |where expr]

show databases;

查看編碼方式

show create database t1;

alter {database|schema} [da_name] [default] character set [=] charset_name

刪除數據庫

drop {database|schema} [if exists] da_name

八、MySQL 數據類型

????????數據類型是指列、存儲過程參數、表達式和局部變量的數據特征，它決定了數據的存儲格式，代表了不同的信息類型。

????????整型

????tinyint 1字節 ?smallint2字節 mediumint3字節 int4字節 bigint8字節

????????浮點型

????float[(M,D)] M是數字總位數，D是小數點后面的位數，如果M和D被省略，根據硬件允許的限制來保存值。大約精確7位小數

double 雙精度浮點

????????日期時間型

????year 1

????time 3

????date 3

????datetime 8

????timestamp 4

????????字符型

????char(M) ?M個字節，0-255

????varchar(M) L+1個字節，L<=M<=65535

????tinytext L+1字節 L<28

????text L+1字節 L<216

????mediumtext() 字節 L+1 L<224

????longtext ?L+1字節 L<232

????enum('vlaue1','value2',...) 1 or 2個字節，取決于枚舉值個數，最多65535

????set('value','value2',...) 1，2，3，4，8個字節，取決于set成員數目，最多64個 集合

九、數據表的操作

數據表是數據庫的最重要組成部分，是對象的基礎

打開數據庫 use db_name

創建數據表

create table [if not exists] table_name(

column_name data_type,

column_name data_type,

)

root@localhost t2>create table if not exists haha(-> id int primary key,-> name varchar(10),-> age tinyint unsigned,-> salary float(8,2) unsigned-> );

Query OK, 0 rows affected (0.87 sec)

查看數據表

show tables [from db_name] [like 'pattern'|where expr]

show tables

root@localhost t2>show tables;

+--------------+| Tables_in_t2 |+--------------+| haha ? ? ? ? |+--------------+1 row in set (0.05 sec)

????????查看數據表結構

show columns from table_name

root@localhost t2>show columns from haha;

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

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

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

| id ? ? | int(11) ? ? ? ? ? ? | NO ? | PRI | NULL ? ?| ? ? ? |

| name ? | varchar(10) ? ? ? ? | YES ?| ? ? | NULL ? ?| ? ? ? |

| age ? ?| tinyint(3) unsigned | YES ?| ? ? | NULL ? ?| ? ? ? |

| salary | float(8,2) unsigned | YES ?| ? ? | NULL ? ?| ? ? ?

|+--------+---------------------+------+-----+---------+-------+

4 rows in set (1.92 sec)

????????插入記錄

insert [into] table_name [(col_name,...)] values(val,....)

root@localhost t2>insert haha values(1,'zhangsan',18,10000.00);

Query OK, 1 row affected (0.49 sec)

root@localhost t2>insert haha(id,name,salary) values(2,'lisi',2002.35);Query OK, 1 row affected (0.08 sec)

查找記錄

select expr,... from table_name

root@localhost t2>select * from t2;

ERROR 1146 (42S02): Table 't2.t2' doesn't existroot@localhost t2>select * from haha;

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

| id | name ? ? | age ?| salary ? |

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

| ?1 | zhangsan | ? 18 | 10000.00 |

| ?2 | lisi ? ? | NULL | ?2002.35 |

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

2 rows in set (0.00 sec)

????????空值與非空

????????null,not null

root@localhost t2>create table tb2( ? ?-> name varchar(20) not null, ? ?-> age tinyint unsigned null ? ?-> );

Query OK, 0 rows affected (0.27 sec)

root@localhost t2>show columns from tb2;

+-------+---------------------+------+-----+---------+-------+|

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

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

| name ?| varchar(20) ? ? ? ? | NO ? | ? ? | NULL ? ?| ? ? ? |

| age ? | tinyint(3) unsigned | YES ?| ? ? | NULL ? ?| ? ? ? |

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

2 rows in set (0.05 sec)

root@localhost t2>insert tb2 vlaues('tom',null);ERROR 1064 (42000): You have an error in your SQL syntax; check the manual thatcorresponds to your MySQL server version for the right syntax to use near 'vlaues('tom',null)' at line 1root@localhost t2>insert tb2 values('tom',null);Query OK, 1 row affected (0.04 sec)

root@localhost t2>insert tb2 values(null,12);ERROR 1048 (23000): Column 'name' cannot be null

root@localhost t2>select * from tb2;

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

| name | age ?|

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

| tom ?| NULL |

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

1 row in set (0.00 sec)

????????自動編號

????auto_increment

????????主鍵 (primary key)

????每張數據表只能存在一個主鍵

????主鍵保證記錄的唯一性(鍵值唯一)

????主鍵自動為not null

root@localhost t2>create table tb3(-> id int unsigned auto_increment primary key,-> username varchar(10) not null-> );

Query OK, 0 rows affected (0.04 sec)

root@localhost t2>show columns from tb3;

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

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

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

| id ? ? ? | int(10) unsigned | NO ? | PRI | NULL ? ?| auto_increment || username | varchar(10) ? ? ?| NO ? | ? ? | NULL ? ?| ? ? ? ? ? ? ? ?|

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

2 rows in set (0.06 sec)

root@localhost t2>insert tb3(username) values('zhangsan');Query OK, 1 row affected (0.03 sec)

root@localhost t2>insert tb3(username) values('lisi');Query OK, 1 row affected (0.00 sec)

root@localhost t2>insert tb3(username) values('wangwu');Query OK, 1 row affected (0.00 sec)

root@localhost t2>insert tb3(username) values('zhaoliu');Query OK, 1 row affected (0.00 sec)

root@localhost t2>select * from tb3;

+----+----------+|

id | username |

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

| ?1 | zhangsan |

| ?2 | lisi ? ? |

| ?3 | wangwu ? |

| ?4 | zhaoliu ?|

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

4 rows in set (0.00 sec)

????????唯一約束(unique key)

????唯一約束保證記錄的唯一性

????唯一約束的字段可以為空值(null)

????每張數據表可以存在多個唯一約束(鍵值唯一)

root@localhost t2>create table tb5(-> id int unsigned auto_increment primary key,-> username varchar(20) not null unique key,-> age tinyint unsigned-> );

Query OK, 0 rows affected (0.07 sec)

root@localhost t2>show columns from tb5;

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

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

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

| id ? ? ? | int(10) unsigned ? ?| NO ? | PRI | NULL ? ?| auto_increment || username | varchar(20) ? ? ? ? | NO ? | UNI | NULL ? ?| ? ? ? ? ? ? ? ?|

| age ? ? ?| tinyint(3) unsigned | YES ?| ? ? | NULL ? ?| ? ? ? ? ? ? ? ?|

+----------+---------------------+------+-----+---------+----------------+3 rows in set (0.06 sec)

root@localhost t2>insert tb5(username,age) values('zhangsan',15);Query OK, 1 row affected (0.00 sec)

root@localhost t2>insert tb5(username,age) values('zhangsan',16);ERROR 1062 (23000): Duplicate entry 'zhangsan' for key 'username'

默認約束(default)

默認值，當插入記錄時，如果沒有明確為字段賦值，則自動賦予默認值

root@localhost t2>create table tb6(-> id int unsigned auto_increment primary key,-> name varchar(10) not null unique key,-> sex enum('1','2','3') default '3'-> );

Query OK, 0 rows affected (0.01 sec)

root@localhost t2>show columns from tb6;

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

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

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

| id ? ?| int(10) unsigned ?| NO ? | PRI | NULL ? ?| auto_increment |

| name ?| varchar(10) ? ? ? | NO ? | UNI | NULL ? ?| ? ? ? ? ? ? ? ?|

| sex ? | enum('1','2','3') | YES ?| ? ? | 3 ? ? ? | ? ? ? ? ? ? ? ?|

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

3 rows in set (0.06 sec)

root@localhost t2>insert tb6(name) values('zhangsan');Query OK, 1 row affected (0.00 sec)

root@localhost t2>select * from tb6;

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

| id | name ? ? | sex ?|

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

| ?1 | zhangsan | 3 ? ?|

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

1 row in set (0.00 sec)

總結

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