Linux学习-MySQL之SQL语句
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MySQL数据类型
- 数值型
- 精确数值
int
decimal
- 近似数值
float
double
real - 字符型
定长：char、binary
变长：varchar、varbinary
text
blob
ENUM,SET - 日期时间型
date,time,datetime,timestamp
数据类型定义
1.值类型
2.占据存储空间
3.定长还是变长
4.如何比较和排序
5.能否索引
#查看数据库服务器的字符集
mysql> show character set;
+----------+-----------------------------+---------------------+--------+
| Charset | Description | Default collation | Maxlen |
+----------+-----------------------------+---------------------+--------+
| big5 | Big5 Traditional Chinese | big5_chinese_ci | 2 |
| dec8 | DEC West European | dec8_swedish_ci | 1 |
| cp850 | DOS West European | cp850_general_ci | 1 |
| hp8 | HP West European | hp8_english_ci | 1 |
| koi8r | KOI8-R Relcom Russian | koi8r_general_ci | 1 |
| latin1 | cp1252 West European | latin1_swedish_ci | 1 |
| latin2 | ISO 8859-2 Central European | latin2_general_ci | 1 |
| swe7 | 7bit Swedish | swe7_swedish_ci | 1 |
| ascii | US ASCII | ascii_general_ci | 1 |
| ujis | EUC-JP Japanese | ujis_japanese_ci | 3 |
| sjis | Shift-JIS Japanese | sjis_japanese_ci | 2 |
| hebrew | ISO 8859-8 Hebrew | hebrew_general_ci | 1 |
| tis620 | TIS620 Thai | tis620_thai_ci | 1 |
| euckr | EUC-KR Korean | euckr_korean_ci | 2 |
| koi8u | KOI8-U Ukrainian | koi8u_general_ci | 1 |
| gb2312 | GB2312 Simplified Chinese | gb2312_chinese_ci | 2 |
| greek | ISO 8859-7 Greek | greek_general_ci | 1 |
| cp1250 | Windows Central European | cp1250_general_ci | 1 |
| gbk | GBK Simplified Chinese | gbk_chinese_ci | 2 |
| latin5 | ISO 8859-9 Turkish | latin5_turkish_ci | 1 |
| armscii8 | ARMSCII-8 Armenian | armscii8_general_ci | 1 |
| utf8 | UTF-8 Unicode | utf8_general_ci | 3 |
| ucs2 | UCS-2 Unicode | ucs2_general_ci | 2 |
| cp866 | DOS Russian | cp866_general_ci | 1 |
| keybcs2 | DOS Kamenicky Czech-Slovak | keybcs2_general_ci | 1 |
| macce | Mac Central European | macce_general_ci | 1 |
| macroman | Mac West European | macroman_general_ci | 1 |
| cp852 | DOS Central European | cp852_general_ci | 1 |
| latin7 | ISO 8859-13 Baltic | latin7_general_ci | 1 |
| utf8mb4 | UTF-8 Unicode | utf8mb4_general_ci | 4 |
| cp1251 | Windows Cyrillic | cp1251_general_ci | 1 |
| utf16 | UTF-16 Unicode | utf16_general_ci | 4 |
| utf16le | UTF-16LE Unicode | utf16le_general_ci | 4 |
| cp1256 | Windows Arabic | cp1256_general_ci | 1 |
| cp1257 | Windows Baltic | cp1257_general_ci | 1 |
| utf32 | UTF-32 Unicode | utf32_general_ci | 4 |
| binary | Binary pseudo charset | binary | 1 |
| geostd8 | GEOSTD8 Georgian | geostd8_general_ci | 1 |
| cp932 | SJIS for Windows Japanese | cp932_japanese_ci | 2 |
| eucjpms | UJIS for Windows Japanese | eucjpms_japanese_ci | 3 |
+----------+-----------------------------+---------------------+--------+
40 rows in set (0.00 sec)
#查看排序规则
mysql> show collation;
+--------------------------+----------+-----+---------+----------+---------+
| Collation | Charset | Id | Default | Compiled | Sortlen |
+--------------------------+----------+-----+---------+----------+---------+
| big5_chinese_ci | big5 | 1 | Yes | Yes | 1 |
| big5_bin | big5 | 84 | | Yes | 1 |
| dec8_swedish_ci | dec8 | 3 | Yes | Yes | 1 |
| dec8_bin | dec8 | 69 | | Yes | 1 |
| cp850_general_ci | cp850 | 4 | Yes | Yes | 1 |
| cp850_bin | cp850 | 80 | | Yes | 1 |
| hp8_english_ci | hp8 | 6 | Yes | Yes | 1 |
| hp8_bin | hp8 | 72 | | Yes | 1 |
| koi8r_general_ci | koi8r | 7 | Yes | Yes | 1 |
| koi8r_bin | koi8r | 74 | | Yes | 1 |
| latin1_german1_ci | latin1 | 5 | | Yes | 1 |
| latin1_swedish_ci | latin1 | 8 | Yes | Yes | 1 |
| latin1_danish_ci | latin1 | 15 | | Yes | 1 |
| latin1_german2_ci | latin1 | 31 | | Yes | 2 |
| latin1_bin | latin1 | 47 | | Yes | 1 |
| latin1_general_ci | latin1 | 48 | | Yes | 1 |
#查看服务器字符集设置
mysql> show variables like '%character%';
+--------------------------+---------------------------------------------------------------+
| Variable_name | Value |
+--------------------------+---------------------------------------------------------------+
| character_set_client | utf8 |
| character_set_connection | utf8 |
| character_set_database | utf8 |
| character_set_filesystem | binary |
| character_set_results | utf8 |
| character_set_server | latin1 |
| character_set_system | utf8 |
| character_sets_dir | /usr/local/mysql-5.6.10-linux-glibc2.5-x86_64/share/charsets/ |
+--------------------------+---------------------------------------------------------------+
8 rows in set (0.00 sec)
SQL模型（数据违反规定时，SQL的处理方式）
- ANSI QUOTES–双引号当单引号使用
- IGNORE_SPACE–忽略空白字符
- STRICT_ALL_TABLES–没有设置此项时，非法数据被允许，设置此项，违反数据规则的，则全部被拒绝，并抛出错误
- STRICT_TRANS_TABLES–不允许向支持事务的表中插入非法数据，并返回错误
- TRADITIONAL
#查看sql_mode
mysql> show global variables like 'sql_mode';
+---------------+------------------------+
| Variable_name | Value |
+---------------+------------------------+
| sql_mode | NO_ENGINE_SUBSTITUTION |
+---------------+------------------------+
1 row in set (0.00 sec)
MySQL服务器变量
- 作用域
全局变量
查看全局变量show global variables
只有root用户可以修改
会话变量
查看会话变量show [session] variables
所有用户可以修改 - 生效时间
可动态调整：不用重启服务器生效,即时调整，即时生效
静态：重启服务器生效,必须写入到配置文件，通过参数传递给mysqld - 动态调整参数生效方式
全局：对当前会话无效，只对新建立的会话有效
会话：即时生效，只对当前会话有效
服务器变量：使用select @@查看变量
mysql> select @@global.sql_mode;
+------------------------+
| @@global.sql_mode |
+------------------------+
| NO_ENGINE_SUBSTITUTION |
+------------------------+
1 row in set (0.00 sec)
设定变量值
SET GLOBAL|SESSION 变量名=值
mysql> set global sql_mode='strict_all_tables';
Query OK, 0 rows affected (0.00 sec)
SQL语句
#创建数据库语法
CREATE DATABASE|schema [IF NOT EXISTS] DB_NAME [CHARSET SET=charset name][collation=collation name]
#创建students数据库
mysql> create database if not exists students character set 'gbk' collate 'gbk_chinese_ci';
Query OK, 1 row affected (0.23 sec)
#查看字符集和排序规则
[root@mail students]# cat db.opt
default-character-set=gbk
default-collation=gbk_chinese_ci
#删除数据库
DROP {DATABASE | SCHEMA} [IF EXISTS] db_name
创建表
- 直接定义一张空表
- 从其它表中查询出数据，并以之创建新表
- 以其它表为模板创建一张空表
CREATE TABLE [IF NOT EXISTS] tb_name (col_name col_definition,constraint) ENGINE [=] engine_name collate [=]collate_name comment[=]comment_name row_format
#创建表
mysql> create table tb1(id int unsigned not null auto_increment primary key,name char(20) not null,age tinyint not null);
Query OK, 0 rows affected (0.24 sec)
mysql> create table tb2(id int unsigned not null auto_increment,name char(20) not null,age tinyint not null,primary key(id));
Query OK, 0 rows affected (0.01 sec)
mysql> create table courses(cid tinyint unsigned not null auto_increment primary key,course varchar(50) not null);
Query OK, 0 rows affected (0.00 sec)
mysql> show table status like 'courses'\\G;
*************************** 1. row ***************************
Name: courses
Engine: InnoDB
Version: 10
Row_format: Compact
Rows: 0
Avg_row_length: 0
Data_length: 16384
Max_data_length: 0
Index_length: 0
Data_free: 0
Auto_increment: 1
Create_time: 2021-06-22 05:26:55
Update_time: NULL
Check_time: NULL
Collation: gbk_chinese_ci
Checksum: NULL
Create_options:
Comment:
1 row in set (0.00 sec)
#创建表时修改engine为MyISAM
mysql> create table courses(cid tinyint unsigned not null auto_increment primary key,course varchar(50) not null) engine=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
Index_length: 1024
Data_free: 0
Auto_increment: 1
Create_time: 2021-06-22 05:28:26
Update_time: 2021-06-22 05:28:26
Check_time: NULL
Collation: gbk_chinese_ci
Checksum: NULL
Create_options:
Comment:
1 row in set (0.00 sec)
#插入数据
mysql> insert into courses(course) values('Hamogong'),('Pixijianfa'),('kuihuabaodian');
Query OK, 3 rows affected (0.00 sec)
Records: 3 Duplicates: 0 Warnings: 0
#显示表索引
mysql> show indexes from courses;
+---------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| 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 | 3 | NULL | NULL | | BTREE | | |
+---------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
1 row in set (0.00 sec)
#通过查询的数据结果，将查询结果创建一张表，并将查询到的数据复制到新表
mysql> create table testcourses select * from courses where cid<=2;
Query OK, 2 rows affected (0.00 sec)
Records: 2 Duplicates: 0 Warnings: 0
mysql> select * from testcourses;
+-----+------------+
| cid | course |
+-----+------------+
| 1 | Hamogong |
| 2 | Pixijianfa |
+-----+------------+
2 rows in set (0.00 sec)
#创建一张表类似于courses
mysql> create table test like courses;
Query OK, 0 rows affected (0.00 sec)
mysql> desc test;
+--------+---------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------+---------------------+------+-----+---------+----------------+
| cid | tinyint(3) unsigned | NO | PRI | NULL | auto_increment |
| course | varchar(50) | NO | | NULL | |
+--------+---------------------+------+-----+---------+----------------+
2 rows in set (0.00 sec)
mysql> desc courses;
+--------+---------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------+---------------------+------+-----+---------+----------------+
| cid | tinyint(3) unsigned | NO | PRI | NULL | auto_increment |
| course | varchar(50) | NO | | NULL | |
+--------+---------------------+------+-----+---------+----------------+
2 rows in set (0.00 sec)
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
# 添加唯一键索引
mysql> desc test;
+--------+---------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------+---------------------+------+-----+---------+----------------+
| cid | tinyint(3) unsigned | NO | PRI | NULL | auto_increment |
| course | varchar(50) | NO | | NULL | |
+--------+---------------------+------+-----+---------+----------------+
2 rows in set (0.00 sec)
mysql> alter table test add unique key(course);
Query OK, 0 rows affected (0.00 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc test;
+--------+---------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------+---------------------+------+-----+---------+----------------+
| cid | tinyint(3) unsigned | NO | PRI | NULL | auto_increment |
| course | varchar(50) | NO | UNI | NULL | |
+--------+---------------------+------+-----+---------+----------------+
2 rows in set (0.00 sec)
#修改表字段
mysql> desc test;
+--------+---------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------+---------------------+------+-----+---------+----------------+
| cid | tinyint(3) unsigned | NO | PRI | NULL | auto_increment |
| course | varchar(50) | NO | UNI | NULL | |
+--------+---------------------+------+-----+---------+----------------+
2 rows in set (0.00 sec)
mysql> alter table test change course courses varchar(50) not null;
Query OK, 0 rows affected (0.00 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc test;
+---------+---------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------+---------------------+------+-----+---------+----------------+
| cid | tinyint(3) unsigned | NO | PRI | NULL | auto_increment |
| courses | varchar(50) | NO | UNI | NULL | |
+---------+---------------------+------+-----+---------+----------------+
2 rows in set (0.00 sec)
#添加新字段
mysql> desc test;
+---------+---------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------+---------------------+------+-----+---------+----------------+
| cid | tinyint(3) unsigned | NO | PRI | NULL | auto_increment |
| courses | varchar(50) | NO | UNI | NULL | |
+---------+---------------------+------+-----+---------+----------------+
2 rows in set (0.00 sec)
mysql> alter table test add starttime date default '2021-06-21';
Query OK, 0 rows affected (0.00 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc test;
+-----------+---------------------+------+-----+------------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-----------+---------------------+------+-----+------------+----------------+
| cid | tinyint(3) unsigned | NO | PRI | NULL | auto_increment |
| courses | varchar(50) | NO | UNI | NULL | |
| starttime | date | YES | | 2021-06-21 | |
+-----------+---------------------+------+-----+------------+----------------+
3 rows in set (0.00 sec)
#修改数据库表名
mysql> alter table test rename to testcourse;
Query OK, 0 rows affected (0.00 sec)
mysql> show tables;
+--------------------+
| Tables_in_students |
+--------------------+
| courses |
| testcourse |
+--------------------+
2 rows in set (0.00 sec)
删除表
DROP [TEMPORARY] TABLE [IF EXISTS]
tbl_name [, tbl_name] …
[RESTRICT | CASCADE]
mysql> create table student(sid int unsigned not null auto_increment primary key,name varchar(30),cid int not null);
Query OK, 0 rows affected (0.00 sec)
mysql> insert into student(name,cid) values('Yue Buqun',2),('Zhang Wuji',1);
Query OK, 2 rows affected (0.00 sec)
Records: 2 Duplicates: 0 Warnings: 0
mysql> select * from student;
+-----+------------+-----+
| sid | name | cid |
+-----+------------+-----+
| 1 | Yue Buqun | 2 |
| 2 | Zhang Wuji | 1 |
+-----+------------+-----+
2 rows in set (0.00 sec)
mysql> select * from courses;
+-----+---------------+
| cid | course |
+-----+---------------+
| 1 | Hamogong |
| 2 | Pixijianfa |
| 3 | kuihuabaodian |
+-----+---------------+
mysql> select Name,course from student,courses where student.cid=courses.cid;
+------------+------------+
| Name | course |
+------------+------------+
| Yue Buqun | Pixijianfa |
| Zhang Wuji | Hamogong |
+------------+------------+
#如果表没有设置外键，则可以插入没有的数据
mysql> insert into student (name,cid) values ('Cheng Jialuo',5);
Query OK, 1 row affected (0.00 sec)
mysql> select * from student;
+-----+--------------+-----+
| sid | name | cid |
+-----+--------------+-----+
| 1 | Yue Buqun | 2 |
| 2 | Zhang Wuji | 1 |
| 3 | Cheng Jialuo | 5 |
+-----+--------------+-----+
3 rows in set (0.00 sec)
mysql> delete from student where cid='5';
Query OK, 1 row affected (0.00 sec)
#给student表添加外键，两个表中的字段类型必须一致，表存储引擎必须支持事务
mysql> alter table student add foreign key(cid) references courses(cid);
Query OK, 2 rows affected (0.23 sec)
Records: 2 Duplicates: 0 Warnings: 0
#查看表索引
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 | cid | 1 | cid | A | 2 | NULL | NULL | | BTREE | | |
+---------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
2 rows in set (0.00 sec)
mysql> select * from courses;
+-----+---------------+
| cid | course |
+-----+---------------+
| 1 | Hamogong |
| 2 | Pixijianfa |
| 3 | kuihuabaodian |
+-----+---------------+
3 rows in set (0.00 sec)
#如果插入的数据，关联的外键没有，则会出现报错
mysql> insert into student(name,cid)values('Chen Jialuo',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`))
#如果数据被其它表中引用，则不能进行删除
mysql> delete from courses where cid ='2';
ERROR 1451 (23000): Cannot delete or update a parent row: a foreign key constraint fails (`students`.`student`, CONSTRAINT `student_ibfk_1` FOREIGN KEY (`cid`) REFERENCES `courses` (`cid`)
#创建索引
mysql> create index name_no_student on student(name) using btree;
Query OK, 0 rows affected (0.03 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 | cid | 1 | cid | A | 2 | NULL | NULL | | BTREE | | |
| student | 1 | name_no_student | 1 | name | A | 2 | NULL | NULL | YES | BTREE | | |
+---------+------------+-----------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
3 rows in set (0.00 sec)
#删除索引
mysql> drop index name_no_student on student;
Query OK, 0 rows affected (0.00 sec)
Records: 0 Duplicates: 0 Warnings: 0
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