mysql03-SQL应用

SQL 基础应用

1.什么是SQL

关系型数据库当中通用的查询语言。全名：结构化查询语言。

2.SQL标准 （ANSI/ISO）

SQL-89
SQL-92 
SQL-99 
SQL-03

3.SQL常用分类

DDL ： 数据定义语言 
DCL ： 数据控制语言
DML ： 数据操作语言

4.SQL_MODE

5.7+之后采用的是严格模式
作用：为了让我们SQL在执行时更加严谨、有意义、符合常识、逻辑、符合科学等
查看SQL_MODE:
mysql> select @@sql_mode;
+-------------------------------------------------------------------------------------------------------------------------------------------+
| @@sql_mode                                                                                                                                |
+-------------------------------------------------------------------------------------------------------------------------------------------+
| ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION |
+-------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
设置SQL_MODE:
mysql> set sql_mode='';
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> select @@sql_mode;
+------------+
| @@sql_mode |
+------------+
|            |
+------------+
1 row in set (0.00 sec)
mysql> set sql_mode='ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION';
Query OK, 0 rows affected, 1 warning (0.00 sec)


mysql> select @@sql_mode;
+-------------------------------------------------------------------------------------------------------------------------------------------+
| @@sql_mode                                                                                                                                |
+-------------------------------------------------------------------------------------------------------------------------------------------+
| ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION |
+-------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

5.字符集和校对规则

5.1字符集
mysql> show charset;
+----------+---------------------------------+---------------------+--------+
| 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 |
| gb18030  | China National Standard GB18030 | gb18030_chinese_ci  |      4 |
+----------+---------------------------------+---------------------+--------+
41 rows in set (0.00 sec)
mysql> show variables like '%char%';
+--------------------------+---------------------------------------------------------------+
| Variable_name            | Value                                                         |
+--------------------------+---------------------------------------------------------------+
| character_set_client     | utf8                                                          |
| character_set_connection | utf8                                                          |
| character_set_database   | utf8mb4                                                       |
| character_set_filesystem | binary                                                        |
| character_set_results    | utf8                                                          |
| character_set_server     | latin1                                                        |
| character_set_system     | utf8                                                          |
| character_sets_dir       | /data/app/mysql-5.7.28-linux-glibc2.12-x86_64/share/charsets/ |
+--------------------------+---------------------------------------------------------------+
8 rows in set (0.00 sec)
utf8  和 utf8mb4 区别？  
例如： 
utf8不完整，emoji表情字符是不支持，utf8mb4是支持的。
根本原因是，utf8 字符最大长度为3字节，utf8mb4是4字节。
5.2校对规则（排序规则）
mysql> show collation;
作用： 影响到了字符串的排序。

6.数据类型

作用：约束存储的数据更加有意义，符合对于这个列的定义

6.1数据类型

类型	字节量	范围
tinyint	1	0-255 -127~128
int	4	0~2^32-1 -231~231-1

6.2字符串类型

char(10)
定长类型的字符串类型。最多存储10个字符。如果存了5个,剩余空间用空格填充
varchar(10)
变长类型的字符串类型。最多存储10个字符。如果存了5个,按需分配存储空间，另外需要1-2字节，存储字符长度。 
怎么选择：一般情况下 变长字符串就用varchar，固定长度一般采用char类型
enum() ： 枚举类型
应用场景： 列中的数据，有限个数的值的时候，并且是有规律。
6.3 时间日期 
DATETIME 
范围为从 1000-01-01 00:00:00.000000 至 9999-12-31 23:59:59.999999。

TIMESTAMP 
1970-01-01 00:00:00.000000 至 2038-01-19 03:14:07.999999。
timestamp会受到时区的影响

7.约束和其他表属性

Primary key ： 主键约束 ，要求设置为主键的列，储值时，非空且唯一。每张表只有一个主键。
not null    :  非空约束，必须录入值
unique key  ： 唯一约束，不能重复值 
unsigned    ： 数字类型约束，无符号。
default        ： 设置默认值，一般配合not null 使用
auto_increment ： 针对数字列，自动增长，一般配合主键
comment        ： 列或者表进行注释

创建库

mysql> create database test1 charset utf8mb4;
Query OK, 1 row affected (0.00 sec)

mysql> create database wordpress1;
Query OK, 1 row affected (0.00 sec)

查询库

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
| test               |
| test1              |
| wordpress1         |
| xiaolai            |
| xuexiao            |
+--------------------+
9 rows in set (0.00 sec)

mysql> show create database test1;
+----------+-------------------------------------------------------------------+
| Database | Create Database                                                   |
+----------+-------------------------------------------------------------------+
| test1    | CREATE DATABASE `test1` /*!40100 DEFAULT CHARACTER SET utf8mb4 */ |
+----------+-------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> show create database wordpress1;
+------------+-----------------------------------------------------------------------+
| Database   | Create Database                                                       |
+------------+-----------------------------------------------------------------------+
| wordpress1 | CREATE DATABASE `wordpress1` /*!40100 DEFAULT CHARACTER SET latin1 */ |
+------------+-----------------------------------------------------------------------+
1 row in set (0.00 sec)

修改库

mysql> show create database wordpress1;
+------------+-----------------------------------------------------------------------+
| Database   | Create Database                                                       |
+------------+-----------------------------------------------------------------------+
| wordpress1 | CREATE DATABASE `wordpress1` /*!40100 DEFAULT CHARACTER SET latin1 */ |
+------------+-----------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> alter database wordpress1 charset utf8mb4;
Query OK, 1 row affected (0.00 sec)

mysql> show create database wordpress1;
+------------+------------------------------------------------------------------------+
| Database   | Create Database                                                        |
+------------+------------------------------------------------------------------------+
| wordpress1 | CREATE DATABASE `wordpress1` /*!40100 DEFAULT CHARACTER SET utf8mb4 */ |
+------------+------------------------------------------------------------------------+
1 row in set (0.00 sec)

删除库（生产环境不要用此命令）

mysql> drop database wordpress1;
Query OK, 0 rows affected (0.02 sec)

mysql> drop database test1;
Query OK, 0 rows affected (0.00 sec)

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sys                |
| test               |
| xiaolai            |
| xuexiao            |
+--------------------+
7 rows in set (0.00 sec)

建表

USE test;
CREATE TABLE stu (
id     INT NOT NULL PRIMARY KEY AUTO_INCREMENT COMMENT '学号',
sname  VARCHAR(64) NOT NULL COMMENT '姓名',
age    TINYINT  UNSIGNED  NOT NULL DEFAULT 0  COMMENT '年龄',
gender ENUM('m','f','n')  NOT NULL DEFAULT 'n' COMMENT '性别',
intime DATETIME NOT NULL COMMENT '入学时间'
)ENGINE=INNODB CHARSET=utf8mb4 COMMENT '学生表';

查表定义

mysql> show tables;
+----------------+
| Tables_in_test |
+----------------+
| stu            |
+----------------+
1 row in set (0.00 sec)
mysql> show create table stu;
+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| stu   | CREATE TABLE `stu` (
  `id` int(11) NOT NULL AUTO_INCREMENT COMMENT '学号',
  `sname` varchar(64) NOT NULL COMMENT '姓名',
  `age` tinyint(3) unsigned NOT NULL DEFAULT '0' COMMENT '年龄',
  `gender` enum('m','f','n') NOT NULL DEFAULT 'n' COMMENT '性别',
  `intime` datetime NOT NULL COMMENT '入学时间',
  `tel` varchar(64) NOT NULL COMMENT '手机号',
  PRIMARY KEY (`id`),
  UNIQUE KEY `telnum` (`tel`),
  UNIQUE KEY `telnum_2` (`tel`),
  UNIQUE KEY `telnum_3` (`tel`),
  UNIQUE KEY `tel` (`tel`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COMMENT='学生表'                   |
+-------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
mysql> desc stu;
+--------+---------------------+------+-----+---------+----------------+
| Field  | Type                | Null | Key | Default | Extra          |
+--------+---------------------+------+-----+---------+----------------+
| id     | int(11)             | NO   | PRI | NULL    | auto_increment |
| sname  | varchar(64)         | NO   |     | NULL    |                |
| age    | tinyint(3) unsigned | NO   |     | 0       |                |
| gender | enum('m','f','n')   | NO   |     | n       |                |
| intime | datetime            | NO   |     | NULL    |                |
| tel    | varchar(64)         | NO   | UNI | NULL    |                |
+--------+---------------------+------+-----+---------+----------------+
6 rows in set (0.00 sec)

修改表定义

-- 添加和删除字段
-- 1. 在表中添加telnum char(11) not null unique key comment '手机号'
mysql> alter table stu add column telnum char(11) not null unique key comment '手机号';
Query OK, 0 rows affected (0.06 sec)
Records: 0  Duplicates: 0  Warnings: 0
mysql> desc stu;
+--------+---------------------+------+-----+---------+----------------+
| Field  | Type                | Null | Key | Default | Extra          |
+--------+---------------------+------+-----+---------+----------------+
| id     | int(11)             | NO   | PRI | NULL    | auto_increment |
| sname  | varchar(64)         | NO   |     | NULL    |                |
| age    | tinyint(3) unsigned | NO   |     | 0       |                |
| gender | enum('m','f','n')   | NO   |     | n       |                |
| intime | datetime            | NO   |     | NULL    |                |
| tel    | varchar(64)         | NO   | UNI | NULL    |                |
| telnum | char(11)            | NO   | UNI | NULL    |                |
+--------+---------------------+------+-----+---------+----------------+
7 rows in set (0.00 sec)
-- 2. 在sname后添加a列
mysql> alter table stu add column a int not null comment '测试列' after sname;
Query OK, 0 rows affected (0.10 sec)
Records: 0  Duplicates: 0  Warnings: 0
-- 3. 在第一列前添加b列
mysql> alter table stu add column b int not null comment '测试列' first;
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0
-- 4. 删除添加的a,b列
mysql> alter table stu drop column a;
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> alter table stu drop column b;
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0
-- 5. 修改数据类型
mysql> alter table stu modify telnum varchar(20) not null unique key comment '手机号';
Query OK, 0 rows affected, 1 warning (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 1
mysql> alter table stu modify telnum varchar(30) not null unique key comment '手机号';
Query OK, 0 rows affected, 1 warning (0.05 sec)
Records: 0  Duplicates: 0  Warnings: 1
-- 6. 修改列名及数据类型
mysql> alter table stu change telnum teg varchar(64) not null unique key comment '手机号';
Query OK, 0 rows affected, 1 warning (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 1
mysql> alter table stu change telnum teg varchar(64) not null unique key comment '手机号';
Query OK, 0 rows affected, 1 warning (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 1

mysql> desc stu;
+--------+---------------------+------+-----+---------+----------------+
| Field  | Type                | Null | Key | Default | Extra          |
+--------+---------------------+------+-----+---------+----------------+
| id     | int(11)             | NO   | PRI | NULL    | auto_increment |
| sname  | varchar(64)         | NO   |     | NULL    |                |
| age    | tinyint(3) unsigned | NO   |     | 0       |                |
| gender | enum('m','f','n')   | NO   |     | n       |                |
| intime | datetime            | NO   |     | NULL    |                |
| tel    | varchar(64)         | NO   | UNI | NULL    |                |
| teg    | varchar(64)         | NO   | UNI | NULL    |                |
+--------+---------------------+------+-----+---------+----------------+
7 rows in set (0.00 sec)

删除表

mysql> drop table stu;
Query OK, 0 rows affected (0.00 sec)
mysql> show tables;
Empty set (0.00 sec)

DDL语句开发规范

库：  CREATE DATABASE test CHARSET utf8mb4;
	1. 库名要与业务有关
	2. 库名不使用大写字母、数字开头。
	3. 不要使用内置关键字
	4. 建库要指定字符集。
	5. 生产中禁止使用删库操作。

表： 
CREATE TABLE stu (
id     INT NOT NULL PRIMARY KEY AUTO_INCREMENT COMMENT '学号',
sname  VARCHAR(64) NOT NULL COMMENT '姓名',
age    TINYINT  UNSIGNED  NOT NULL DEFAULT 0  COMMENT '年龄',
gender ENUM('m','f','n')  NOT NULL DEFAULT 'n' COMMENT '性别',
intime DATETIME NOT NULL COMMENT '入学时间'
)ENGINE=INNODB CHARSET=utf8mb4 COMMENT '学生表';

1. 表名：与业务有关,例如：wp_users，不使用大写字母、数字开头，不要太长（16以下）
2. 设置存储引擎、字符集、表注释   
3. 表名、列名要使用内置关键字
4. 列名要有意义，长度（16以下）
5. 数据类型：合适的、足够的、简短
6. 每个表要有主键，一般是自增长、无关列数字列。
7. 每个列尽量是not null ，可以配合default
8. 每个列要有注释
9. 修改定义的操作，要在业务不繁忙期间去做。如果紧急可以使用pt-osc 。