1. SQL语言

1.1 关系型数据库的常见组件

	数据库：database
	表：table，行：row 列：column
	索引：index
	视图：view
	用户：user
	权限：privilege
	存储过程：procedure
	存储函数：function
	触发器：trigger
	事件调度器：event scheduler，任务计划

1.2 SQL语言规范

	在数据库系统中，SQL语句不区分大小写(建议用大写)
	SQL语句可单行或多行书写，以“;”结尾
	关键词不能跨多行或简写
	用空格和缩进来提高语句的可读性
	子句通常位于独立行，便于编辑，提高可读性
	注释：
		SQL标准：
			-- 注释内容 单行注释，注意有空格
			/*注释内容*/ 多行注释
		MySQL注释：
			#

1.3 SQL语句分类 # （重点内容）

1.3.1 DDL: Data Defination Language 数据定义语言

	CREATE，DROP，ALTER

1.3.1.1 创建表

	CREATE TABLE

CREATE TABLE 表名称
(
列名称1 数据类型,
列名称2 数据类型,
列名称3 数据类型,
....
)

MariaDB [mysql]> create database school;
Query OK, 1 row affected (0.00 sec)

MariaDB [mysql]> 
MariaDB [mysql]> 
MariaDB [mysql]> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| school             |
+--------------------+
4 rows in set (0.00 sec)
MariaDB [mysql]> use school;
Database changed
MariaDB [school]> show tables;
Empty set (0.00 sec）
MariaDB [school]> create table student(
    -> StuID int(10) unsigned not null auto_increment primary key,
    -> Name varchar(50) not null,
    -> Gender enum('F', 'M') not null
    -> ) engine=InnoDB default charset=utf8;
Query OK, 0 rows affected (0.01 sec)

MariaDB [school]> 
MariaDB [school]> show tables;
+------------------+
| Tables_in_school |
+------------------+
| student          |
+------------------+
1 row in set (0.01 sec)

1.3.1.2 查看表

1.查看支持的engine类型：SHOW ENGINES;

MariaDB [hellodb]> show engines;
+--------------------+---------+----------------------------------------------------------------------------------+--------------+------+------------+
| Engine             | Support | Comment                                                                          | Transactions | XA   | Savepoints |
+--------------------+---------+----------------------------------------------------------------------------------+--------------+------+------------+
| CSV                | YES     | Stores tables as CSV files                                                       | NO           | NO   | NO         |
| MRG_MyISAM         | YES     | Collection of identical MyISAM tables                                            | NO           | NO   | NO         |
| MyISAM             | YES     | Non-transactional engine with good performance and small data footprint          | NO           | NO   | NO         |
| SEQUENCE           | YES     | Generated tables filled with sequential values                                   | YES          | NO   | YES        |
| PERFORMANCE_SCHEMA | YES     | Performance Schema                                                               | NO           | NO   | NO         |
| MEMORY             | YES     | Hash based, stored in memory, useful for temporary tables                        | NO           | NO   | NO         |
| Aria               | YES     | Crash-safe tables with MyISAM heritage                                           | NO           | NO   | NO         |
| InnoDB             | DEFAULT | Supports transactions, row-level locking, foreign keys and encryption for tables | YES          | YES  | YES        |
+--------------------+---------+----------------------------------------------------------------------------------+--------------+-----

查看表：SHOW TABLES [FROM db_name]

MariaDB [hellodb]> show tables; #当然这里已经切换到databses的hellodb数据库
+-------------------+
| Tables_in_hellodb |
+-------------------+
| classes           |
| coc               |
| courses           |
| scores            |
| students          |
| teachers          |
| toc               |
+-------------------+
7 rows in set (0.00 sec)

查看表结构：DESC [db_name.]tb_name，SHOW COLUMNS FROM [db_name.]tb_name

MariaDB [hellodb]> desc students;
+-----------+---------------------+------+-----+---------+----------------+
| Field     | Type                | Null | Key | Default | Extra          |
+-----------+---------------------+------+-----+---------+----------------+
| StuID     | int(10) unsigned    | NO   | PRI | NULL    | auto_increment |
| Name      | varchar(50)         | NO   | MUL | NULL    |                |
| Age       | tinyint(3) unsigned | NO   |     | NULL    |                |
| Gender    | enum('F','M')       | NO   |     | NULL    |                |
| ClassID   | tinyint(3) unsigned | YES  |     | NULL    |                |
| TeacherID | int(10) unsigned    | YES  |     | NULL    |                |
+-----------+---------------------+------+-----+---------+----------------+
6 rows in set (0.08 sec)

查看表创建命令：

MariaDB [hellodb]> show create table students\G;
*************************** 1. row ***************************
       Table: students
Create Table: CREATE TABLE `students` (
  `StuID` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `Name` varchar(50) NOT NULL,
  `Age` tinyint(3) unsigned NOT NULL,
  `Gender` enum('F','M') NOT NULL,
  `ClassID` tinyint(3) unsigned DEFAULT NULL,
  `TeacherID` int(10) unsigned DEFAULT NULL,
  PRIMARY KEY (`StuID`),
  KEY `ind_name` (`Name`(5))
) ENGINE=InnoDB AUTO_INCREMENT=26 DEFAULT CHARSET=utf8
1 row in set (0.01 sec)

修改和删除表
修改表

MariaDB [school]> desc student;
+--------+------------------+------+-----+---------+----------------+
| Field  | Type             | Null | Key | Default | Extra          |
+--------+------------------+------+-----+---------+----------------+
| StuID  | int(10) unsigned | NO   | PRI | NULL    | auto_increment |
| Name   | varchar(50)      | NO   |     | NULL    |                |
| Gender | enum('F','M')    | NO   |     | NULL    |                |
+--------+------------------+------+-----+---------+----------------+
3 rows in set (0.00 sec)

MariaDB [school]> 
MariaDB [school]> alter table student add phone varchar(50) not null; #
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0

MariaDB [school]> 
MariaDB [school]>
MariaDB [school]> desc student;
+--------+------------------+------+-----+---------+----------------+
| Field  | Type             | Null | Key | Default | Extra          |
+--------+------------------+------+-----+---------+----------------+
| StuID  | int(10) unsigned | NO   | PRI | NULL    | auto_increment |
| Name   | varchar(50)      | NO   |     | NULL    |                |
| Gender | enum('F','M')    | NO   |     | NULL    |                |
| phone  | varchar(50)      | NO   |     | NULL    |                |
+--------+------------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)

删除表

MariaDB [school]> desc student;
+--------+------------------+------+-----+---------+----------------+
| Field  | Type             | Null | Key | Default | Extra          |
+--------+------------------+------+-----+---------+----------------+
| StuID  | int(10) unsigned | NO   | PRI | NULL    | auto_increment |
| Name   | varchar(50)      | NO   |     | NULL    |                |
| Gender | enum('F','M')    | NO   |     | NULL    |                |
+--------+------------------+------+-----+---------+----------------+
3 rows in set (0.00 sec)

MariaDB [school]> 
MariaDB [school]> drop table student; #
Query OK, 0 rows affected (0.01 sec)

MariaDB [school]> show tables;
Empty set (0.00 sec)

1.3.2 DML: Data Manipulation Language 数据操纵语言

	INSERT，DELETE，UPDATE

1.3.2.1 INSERT 语句

简化写法：INSERT tbl_name [(col1,...)] VALUES (val1,...), (val21,...)
举例：

MariaDB [school]> select * from student;
Empty set (0.00 sec)

MariaDB [school]> 
MariaDB [school]> desc student;
+-------+------------------+------+-----+---------+----------------+
| Field | Type             | Null | Key | Default | Extra          |
+-------+------------------+------+-----+---------+----------------+
| StuID | int(10) unsigned | NO   | PRI | NULL    | auto_increment |
| Name  | varchar(20)      | YES  |     | NULL    |                |
| phone | varchar(20)      | NO   |     | NULL    |                |
+-------+------------------+------+-----+---------+----------------+
3 rows in set (0.00 sec)

MariaDB [school]>
MariaDB [school]>
MariaDB [school]> insert into student (Name, phone) values ("gordon", "15201039555");
Query OK, 1 row affected (0.00 sec)

MariaDB [school]> select * from student;
+-------+--------+-------------+
| StuID | Name   | phone       |
+-------+--------+-------------+
|     1 | gordon | 15201039555 |
+-------+--------+-------------+
1 row in set (0.00 sec)

1.3.2.2 UPDATE 语句

语法：

UPDATE [LOW_PRIORITY] [IGNORE] table_reference
SET col_name1={expr1|DEFAULT} [, col_name2={expr2|DEFAULT}] ...
[WHERE where_condition]
[ORDER BY ...]
[LIMIT row_count]

注意：一定要有限制条件，否则将修改所有行的指定字段
可利用mysql 选项避免此错误：mysql -U | --safe-updates| --i-am-a-dummy

举例：

update student set Name="The king of night" where phone="15201039554";
Query OK, 1 row affected (0.01 sec)
Rows matched: 1  Changed: 1  Warnings: 0

MariaDB [school]> select * from student;
+-------+-------------------+-------------+
| StuID | Name              | phone       |
+-------+-------------------+-------------+
|     5 | alice             | 15201039551 |
|     6 | tina              | 15201039552 |
|     8 | The king of night | 15201039554 |
+-------+-------------------+-------------+

1.3.2.3 DELETE语句

删除表中数据，但不会自动缩减数据文件的大小
语法:

DELETE [LOW_PRIORITY] [QUICK] [IGNORE] FROM tbl_name
[WHERE where_condition]
[ORDER BY ...]
[LIMIT row_count]
可先排序再指定删除的行数

注意：一定要有限制条件，否则将清空表中的所有数据
如果想清空表，保留表结构，也可以使用下面语句，此语句会自动缩减数据文件的大小。
举例：

MariaDB [school]> select * from student;
+-------+--------+-------------+
| StuID | Name   | phone       |
+-------+--------+-------------+
|     1 | gordon | 15201039555 |
|     2 | gordon | 15201039555 |
+-------+--------+-------------+
2 rows in set (0.00 sec)

MariaDB [school]> 
MariaDB [school]> 
MariaDB [school]> delete from student;
Query OK, 2 rows affected (0.02 sec)

MariaDB [school]> select * from student;
+-------+--------------+-------------+
| StuID | Name         | phone       |
+-------+--------------+-------------+
|     3 | gordon       | 15201039555 |
|     4 | mary         | 15201039555 |
|     5 | alice        | 15201039551 |
|     6 | tina         | 15201039552 |
|     7 | dragon       | 15201039553 |
|     8 | night’s king | 15201039554 |
+-------+--------------+-------------+
6 rows in set (0.00 sec)

MariaDB [school]> 
MariaDB [school]> delete from student where Name="dragon";
Query OK, 1 row affected (0.00 sec)

MariaDB [school]> 
MariaDB [school]> select * from student;
+-------+--------------+-------------+
| StuID | Name         | phone       |
+-------+--------------+-------------+
|     3 | gordon       | 15201039555 |
|     4 | mary         | 15201039555 |
|     5 | alice        | 15201039551 |
|     6 | tina         | 15201039552 |
|     8 | night‘s king | 15201039554 |
+-------+--------------+-------------+

缩减表大小OPTIMIZE TABLE tb_name

1.3.3 DQL：Data Query Language 数据查询语言

1.3.3.1 单表操作

SELECT
语法：

SELECT
[ALL | DISTINCT | DISTINCTROW ]
[SQL_CACHE | SQL_NO_CACHE]
select_expr [, select_expr ...]
[FROM table_references
[WHERE where_condition]
[GROUP BY {col_name | expr | position}
[ASC | DESC], ... [WITH ROLLUP]]
[HAVING where_condition]
[ORDER BY {col_name | expr | position}
[ASC | DESC], ...]
[LIMIT {[offset,] row_count | row_count OFFSET offset}]
[FOR UPDATE | LOCK IN SHARE MODE]

说明：

字段显示可以使用别名：col1 AS alias1, col2 AS alias2, …
WHERE子句：指明过滤条件以实现“选择”的功能：
过滤条件：布尔型表达式
算术操作符：+, -, *, /, %
mysql -U | --safe-updates| --i-am-a-dummy
DELETE [LOW_PRIORITY] [QUICK] [IGNORE] FROM tbl_name
[WHERE where_condition]
[ORDER BY …]
[LIMIT row_count]
可先排序再指定删除的行数

TRUNCATE TABLE tbl_name;
OPTIMIZE TABLE tb_name
SELECT
[ALL | DISTINCT | DISTINCTROW ]
[SQL_CACHE | SQL_NO_CACHE]
select_expr [, select_expr …]
[FROM table_references
[WHERE where_condition]
[GROUP BY {col_name | expr | position}
[ASC | DESC], … [WITH ROLLUP]]
[HAVING where_condition]
[ORDER BY {col_name | expr | position}
[ASC | DESC], …]
[LIMIT {[offset,] row_count | row_count OFFSET offset}]
[FOR UPDATE | LOCK IN SHARE MODE]
比较操作符：=,<=>（相等或都为空）, <>, !=(非标准SQL), >, >=, <, <=
BETWEEN min_num AND max_num
IN (element1, element2, …)
IS NULL
IS NOT NULL
DISTINCT 去除重复列，范例：SELECT DISTINCT gender FROM students;
LIKE:
% 任意长度的任意字符
_ 任意单个字符
RLIKE：正则表达式，索引失效，不建议使用
REGEXP：匹配字符串可用正则表达式书写模式，同上
逻辑操作符：NOT，AND，OR，XOR
GROUP：根据指定的条件把查询结果进行“分组”以用于做“聚合”运算
常见聚合函数：avg(), max(), min(), count(), sum()
HAVING: 对分组聚合运算后的结果指定过滤条件
ORDER BY: 根据指定的字段对查询结果进行排序
升序：ASC
降序：DESC
LIMIT [[offset,]row_count]：对查询的结果进行输出行数数量限制
对查询结果中的数据请求施加“锁”
FOR UPDATE: 写锁，独占或排它锁，只有一个读和写操作
LOCK IN SHARE MODE: 读锁，共享锁，同时多个读操作

DESC students;
INSERT INTO students VALUES(1,'tom'，'m'),(2,'alice','f');
INSERT INTO students(id,name) VALUES(3,'jack'),(4,'allen');
SELECT * FROM students WHERE id < 3;
SELECT * FROM students WHERE gender='m';
SELECT * FROM students WHERE gender IS NULL;
SELECT * FROM students WHERE gender IS NOT NULL;
SELECT * FROM students ORDER BY name DESC LIMIT 2;
SELECT * FROM students ORDER BY name DESC LIMIT 1,2;
SELECT * FROM students WHERE id >=2 and id <=4
SELECT * FROM students WHERE BETWEEN 2 AND 4
SELECT * FROM students WHERE name LIKE ‘t%’
SELECT * FROM students WHERE name RLIKE '.*[lo].*';
SELECT id stuid,name as stuname FROM students
select * from students where classid in (1,3,5);
select classid,avg(age) as 平均年龄 from students where classid > 3 group by
classid having 平均年龄 >30 ;

select classid,sum(age) from students where classid is not null group by
classid order by classid;
select classid,sum(age) from students group by classid having classid is not
null order by classid;
select classid,sum(age) from students where classid is not null group by
classid order by classid limit 2,3;
select gender,avg(age) 平均年龄 from students group by gender having
gender='M';
select classid,gender,avg(age) from students group by classid,gender;
#对classid 正序排序，NULL记录排在最后
select *from students order by -classid desc ;
#多列排序
select * from students order by gender desc, age asc;
#必须先过滤，再排序
select * from students where classid is not null order by gender desc, age asc ;
#分组后再排序
MariaDB [hellodb]> select gender,classid,avg(age) from students where classid is
not null group by gender,classid order by gender,classid;
+--------+---------+----------+
| gender | classid | avg(age) |
+--------+---------+----------+
| F | 1 | 19.0000 |
| F | 3 | 18.3333 |
| F | 6 | 20.0000 |
| F | 7 | 18.0000 |
| F | 77 | 18.0000 |
| F | 93 | 18.0000 |
| M | 1 | 21.5000 |
| M | 2 | 35.2000 |
| M | 3 | 23.0000 |
| M | 4 | 23.6000 |
| M | 5 | 46.0000 |
| M | 6 | 23.0000 |
| M | 7 | 23.0000 |
| M | 94 | 18.0000 |
+--------+---------+----------+
14 rows in set (0.001 sec)

MariaDB [hellodb]> select * from students order by age limit 10;
+-------+---------------+-----+--------+---------+-----------+
| StuID | Name | Age | Gender | ClassID | TeacherID |
+-------+---------------+-----+--------+---------+-----------+
| 14 | Lu Wushuang | 17 | F | 3 | NULL |
| 8 | Lin Daiyu | 17 | F | 7 | NULL |
| 33 | Miejue Shitai | 18 | F | 77 | NULL |
| 32 | Zhang Sanfeng | 18 | M | 94 | NULL |
| 27 | liudehua | 18 | F | 1 | NULL |
| 34 | Lin Chaoying | 18 | F | 93 | NULL |
| 19 | Xue Baochai | 18 | F | 6 | NULL |
| 7 | Xi Ren | 19 | F | 3 | NULL |
| 12 | Wen Qingqing | 19 | F | 1 | NULL |
| 20 | Diao Chan | 19 | F | 7 | NULL |
+-------+---------------+-----+--------+---------+-----------+
10 rows in set (0.001 sec)

MariaDB [hellodb]> select * from students order by age limit 3,10;
+-------+---------------+-----+--------+---------+-----------+
| StuID | Name | Age | Gender | ClassID | TeacherID |
+-------+---------------+-----+--------+---------+-----------+
| 34 | Lin Chaoying | 18 | F | 93 | NULL |
| 19 | Xue Baochai | 18 | F | 6 | NULL |
| 32 | Zhang Sanfeng | 18 | M | 94 | NULL |
| 27 | liudehua | 18 | F | 1 | NULL |
| 20 | Diao Chan | 19 | F | 7 | NULL |
| 12 | Wen Qingqing | 19 | F | 1 | NULL |
| 10 | Yue Lingshan | 19 | F | 3 | NULL |
| 15 | Duan Yu | 19 | M | 4 | NULL |
| 7 | Xi Ren | 19 | F | 3 | NULL |
| 29 | wuyanzu | 19 | M | 4 | NULL |
+-------+---------------+-----+--------+---------+-----------+
10 rows in set (0.000 sec)

MariaDB [hellodb]> select distinct age from students order by age limit 3 ;
+-----+
| age |
+-----+
| 17 |
| 18 |
| 19 |
+-----+
3 rows in set (0.001 sec)
MariaDB [hellodb]> select distinct age from students order by age limit 3,5 ;
+-----+
| age |
+-----+
| 20 |
| 21 |
| 22 |
| 23 |
| 25 |
+-----+
5 rows in set (0.001 sec)

1.3.3.2 多表操作

查询结果来自于多张表，即多表查询

先理解这张牛逼大图
在这里插入图片描述

子查询
常用在WHERE子句中的子查询：
1. 用于比较表达式中的子查询；子查询仅能返回单个值：SELECT Name,Age FROM students WHERE Age>(SELECT avg(Age) FROM students);
2. 用于IN中的子查询：子查询应该单键查询并返回一个或多个值从构成列表：SELECT Name,Age FROM students WHERE Age IN (SELECT Age FROM teachers);
3. 用于EXISTS
4. 用于FROM子句中的子查询：SELECT tb_alias.col1,... FROM (SELECT clause) AS tb_alias WHERE Clause;
  范例：

MariaDB [hellodb]> SELECT s.aage,s.ClassID FROM (SELECT avg(Age) AS aage,ClassID FROM students
    -> WHERE ClassID IS NOT NULL GROUP BY ClassID) AS s WHERE s.aage>30;
+---------+---------+
| aage    | ClassID |
+---------+---------+
| 36.0000 |       2 |
| 46.0000 |       5 |
+---------+---------+
2 rows in set (0.19 sec)

联合查询：UNION

	SELECT Name,Age FROM students UNION SELECT Name,Age FROM teachers;

范例：

#子查询：select 的执行结果，被其它SQL调用
MariaDB [hellodb]> select stuid,name,age from students where age > (select
avg(age) from students);
+-------+--------------+-----+
| stuid | name | age |
+-------+--------------+-----+
| 3 | Xie Yanke | 53 |
| 4 | Ding Dian | 32 |
| 6 | Shi Qing | 46 |
| 13 | Tian Boguang | 33 |
| 25 | Sun Dasheng | 100 |
+-------+--------------+-----+
5 rows in set (0.00 sec)

MariaDB [hellodb]> update teachers set age=(select avg(age) from students) where
tid=4;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
MariaDB [hellodb]> select * from teachers;
+-----+---------------+-----+--------+
| TID | Name | Age | Gender |
+-----+---------------+-----+--------+
| 1 | Song Jiang | 45 | M |
| 2 | Zhang Sanfeng | 94 | M |
| 3 | Miejue Shitai | 77 | F |
| 4 | Lin Chaoying | 27 | F |
+-----+---------------+-----+--------+
4 rows in set (0.00 sec)

#多表纵向合并union
MariaDB [hellodb]> select * from teachers union select * from students;
MariaDB [hellodb]> select tid as id,name,age,gender from teachers union select
stuid,name,age,gender from students;
+----+---------------+-----+--------+
| id | name | age | gender |
+----+---------------+-----+--------+
| 1 | Song Jiang | 45 | M |
| 2 | Zhang Sanfeng | 94 | M |
| 3 | Miejue Shitai | 77 | F |
| 4 | Lin Chaoying | 26 | F |
| 1 | Shi Zhongyu | 22 | M |
| 2 | Shi Potian | 22 | M |
| 3 | Xie Yanke | 53 | M |
| 4 | Ding Dian | 32 | M |
| 5 | Yu Yutong | 26 | M |
| 6 | Shi Qing | 46 | M |
.....省略........

MariaDB [hellodb]> select * from user union select * from user;  
+------+----------+----------+
| id | username | password |
+------+----------+----------+
| 1 | admin | magedu |
| 2 | mage | magedu |
| 3 | wang | centos |
+------+----------+----------+
3 rows in set (0.00 sec)

**#横向合并，交叉连接（横向笛卡尔）**
MariaDB [hellodb]> select * from students cross join teachers;
MariaDB [hellodb]> select * from teachers , students;
+-----+---------------+-----+--------+-------+---------------+-----+--------+---
------+-----------+
| TID | Name | Age | Gender | StuID | Name | Age | Gender |
ClassID | TeacherID |
+-----+---------------+-----+--------+-------+---------------+-----+--------+---
------+-----------+
| 1 | Song Jiang | 45 | M | 1 | Shi Zhongyu | 22 | M |
2 | 3 |
| 2 | Zhang Sanfeng | 94 | M | 1 | Shi Zhongyu | 22 | M |
2 | 3 |
| 3 | Miejue Shitai | 77 | F | 1 | Shi Zhongyu | 22 | M |
2 | 3 |
| 4 | Lin Chaoying | 26 | F | 1 | Shi Zhongyu | 22 | M |
2 | 3 |
| 1 | Song Jiang | 45 | M | 2 | Shi Potian | 22 | M |
1 | 7 |
| 2 | Zhang Sanfeng | 94 | M | 2 | Shi Potian | 22 | M |
1 | 7 |
| 3 | Miejue Shitai | 77 | F | 2 | Shi Potian | 22 | M |
1 | 7 |
| 4 | Lin Chaoying | 26 | F | 2 | Shi Potian | 22 | M |
1 | 7 |
| 1 | Song Jiang | 45 | M | 3 | Xie Yanke | 53 | M |

**#内连接inner join**
MariaDB [hellodb]> select * from students inner join teachers on
students.teacherid=teachers.tid;
+-------+-------------+-----+--------+---------+-----------+-----+--------------
-+-----+--------+
| StuID | Name | Age | Gender | ClassID | TeacherID | TID | Name
| Age | Gender |
+-------+-------------+-----+--------+---------+-----------+-----+--------------
-+-----+--------+
| 5 | Yu Yutong | 26 | M | 3 | 1 | 1 | Song Jiang
| 45 | M |
| 1 | Shi Zhongyu | 22 | M | 2 | 3 | 3 | Miejue Shitai
| 77 | F |
| 4 | Ding Dian | 32 | M | 4 | 4 | 4 | Lin Chaoying
| 93 | F |
+-------+-------------+-----+--------+---------+-----------+-----+--------------
-+-----+--------+

#内连接后过滤数据
MariaDB [hellodb]> select * from students s inner join teachers t on
s.teacherid=t.tid and s.age > 30 ;
+-------+-------------+-----+--------+---------+-----------+-----+--------------
+-----+--------+
| StuID | Name | Age | Gender | ClassID | TeacherID | TID | Name
| Age | Gender |
+-------+-------------+-----+--------+---------+-----------+-----+--------------
+-----+--------+
| 25 | Sun Dasheng | 100 | M | NULL | 1 | 1 | Song Jiang
| 45 | M |
| 4 | Ding Dian | 32 | M | 4 | 4 | 4 | Lin Chaoying
| 26 | F |
+-------+-------------+-----+--------+---------+-----------+-----+--------------
+-----+--------+
2 rows in set (0.002 sec)

**#左外连接**
MariaDB [hellodb]>  select s.stuid,s.name,s.age,s.teacherid,t.tid,t.name,t.age from students as s left outer join teachers as t on s.teacherid=t.tid;
+-------+---------------+-----+-----------+------+---------------+------+
| stuid | name          | age | teacherid | tid  | name          | age  |
+-------+---------------+-----+-----------+------+---------------+------+
|     1 | Shi Zhongyu   |  22 |         3 |    3 | Miejue Shitai |   77 |
|     2 | Shi Potian    |  22 |         7 | NULL | NULL          | NULL |
|     3 | Xie Yanke     |  53 |        16 | NULL | NULL          | NULL |
|     4 | Ding Dian     |  32 |         4 |    4 | Lin Chaoying  |   93 |
|     5 | Yu Yutong     |  26 |         1 |    1 | Song Jiang    |   45 |
|     6 | Shi Qing      |  46 |      NULL | NULL | NULL          | NULL |
|     7 | Xi Ren        |  19 |      NULL | NULL | NULL          | NULL |
|     8 | Lin Daiyu     |  17 |      NULL | NULL | NULL          | NULL |
|     9 | Ren Yingying  |  20 |      NULL | NULL | NULL          | NULL |
|    10 | Yue Lingshan  |  19 |      NULL | NULL | NULL          | NULL |
|    11 | Yuan Chengzhi |  23 |      NULL | NULL | NULL          | NULL |
|    12 | Wen Qingqing  |  19 |      NULL | NULL | NULL          | NULL |
|    13 | Tian Boguang  |  33 |      NULL | NULL | NULL          | NULL |
|    14 | Lu Wushuang   |  17 |      NULL | NULL | NULL          | NULL |
|    15 | Duan Yu       |  19 |      NULL | NULL | NULL          | NULL |
|    16 | Xu Zhu        |  21 |      NULL | NULL | NULL          | NULL |
|    17 | Lin Chong     |  25 |      NULL | NULL | NULL          | NULL |
|    18 | Hua Rong      |  23 |      NULL | NULL | NULL          | NULL |
|    19 | Xue Baochai   |  18 |      NULL | NULL | NULL          | NULL |
|    20 | Diao Chan     |  19 |      NULL | NULL | NULL          | NULL |
|    21 | Huang Yueying |  22 |      NULL | NULL | NULL          | NULL |
|    22 | Xiao Qiao     |  20 |      NULL | NULL | NULL          | NULL |
|    23 | Ma Chao       |  23 |      NULL | NULL | NULL          | NULL |
|    24 | Xu Xian       |  27 |      NULL | NULL | NULL          | NULL |
|    25 | Sun Dasheng   | 100 |      NULL | NULL | NULL          | NULL |
+-------+---------------+-----+-----------+------+---------------+------+

```bash
**#左外连接扩展**
MariaDB [hellodb]> select * from students s left outer join teachers t on s.teacherid=t.tid where t.tid is null;
+-------+---------------+-----+--------+---------+-----------+------+------+------+--------+
| StuID | Name          | Age | Gender | ClassID | TeacherID | TID  | Name | Age  | Gender |
+-------+---------------+-----+--------+---------+-----------+------+------+------+--------+
|     2 | Shi Potian    |  22 | M      |       1 |         7 | NULL | NULL | NULL | NULL   |
|     3 | Xie Yanke     |  53 | M      |       2 |        16 | NULL | NULL | NULL | NULL   |
|     6 | Shi Qing      |  46 | M      |       5 |      NULL | NULL | NULL | NULL | NULL   |
|     7 | Xi Ren        |  19 | F      |       3 |      NULL | NULL | NULL | NULL | NULL   |
|     8 | Lin Daiyu     |  17 | F      |       7 |      NULL | NULL | NULL | NULL | NULL   |
|     9 | Ren Yingying  |  20 | F      |       6 |      NULL | NULL | NULL | NULL | NULL   |
|    10 | Yue Lingshan  |  19 | F      |       3 |      NULL | NULL | NULL | NULL | NULL   |
|    11 | Yuan Chengzhi |  23 | M      |       6 |      NULL | NULL | NULL | NULL | NULL   |
|    12 | Wen Qingqing  |  19 | F      |       1 |      NULL | NULL | NULL | NULL | NULL   |
|    13 | Tian Boguang  |  33 | M      |       2 |      NULL | NULL | NULL | NULL | NULL   |
|    14 | Lu Wushuang   |  17 | F      |       3 |      NULL | NULL | NULL | NULL | NULL   |
|    15 | Duan Yu       |  19 | M      |       4 |      NULL | NULL | NULL | NULL | NULL   |
|    16 | Xu Zhu        |  21 | M      |       1 |      NULL | NULL | NULL | NULL | NULL   |
|    17 | Lin Chong     |  25 | M      |       4 |      NULL | NULL | NULL | NULL | NULL   |
|    18 | Hua Rong      |  23 | M      |       7 |      NULL | NULL | NULL | NULL | NULL   |
|    19 | Xue Baochai   |  18 | F      |       6 |      NULL | NULL | NULL | NULL | NULL   |
|    20 | Diao Chan     |  19 | F      |       7 |      NULL | NULL | NULL | NULL | NULL   |
|    21 | Huang Yueying |  22 | F      |       6 |      NULL | NULL | NULL | NULL | NULL   |
|    22 | Xiao Qiao     |  20 | F      |       1 |      NULL | NULL | NULL | NULL | NULL   |
|    23 | Ma Chao       |  23 | M      |       4 |      NULL | NULL | NULL | NULL | NULL   |
|    24 | Xu Xian       |  27 | M      |    NULL |      NULL | NULL | NULL | NULL | NULL   |
|    25 | Sun Dasheng   | 100 | M      |    NULL |      NULL | NULL | NULL | NULL | NULL   |
+-------+---------------+-----+--------+---------+-----------+------+------+------+--------+
22 rows in set (0.00 sec)

**#多个条件的左外连接**
MariaDB [hellodb]> select * from students s left outer join teachers t on s.teacherid=t.tid and s.teacherid is null;
+-------+---------------+-----+--------+---------+-----------+------+------+------+--------+
| StuID | Name          | Age | Gender | ClassID | TeacherID | TID  | Name | Age  | Gender |
+-------+---------------+-----+--------+---------+-----------+------+------+------+--------+
|     1 | Shi Zhongyu   |  22 | M      |       2 |         3 | NULL | NULL | NULL | NULL   |
|     2 | Shi Potian    |  22 | M      |       1 |         7 | NULL | NULL | NULL | NULL   |
|     3 | Xie Yanke     |  53 | M      |       2 |        16 | NULL | NULL | NULL | NULL   |
|     4 | Ding Dian     |  32 | M      |       4 |         4 | NULL | NULL | NULL | NULL   |
|     5 | Yu Yutong     |  26 | M      |       3 |         1 | NULL | NULL | NULL | NULL   |
|     6 | Shi Qing      |  46 | M      |       5 |      NULL | NULL | NULL | NULL | NULL   |
|     7 | Xi Ren        |  19 | F      |       3 |      NULL | NULL | NULL | NULL | NULL   |
|     8 | Lin Daiyu     |  17 | F      |       7 |      NULL | NULL | NULL | NULL | NULL   |
|     9 | Ren Yingying  |  20 | F      |       6 |      NULL | NULL | NULL | NULL | NULL   |
|    10 | Yue Lingshan  |  19 | F      |       3 |      NULL | NULL | NULL | NULL | NULL   |
|    11 | Yuan Chengzhi |  23 | M      |       6 |      NULL | NULL | NULL | NULL | NULL   |
|    12 | Wen Qingqing  |  19 | F      |       1 |      NULL | NULL | NULL | NULL | NULL   |
|    13 | Tian Boguang  |  33 | M      |       2 |      NULL | NULL | NULL | NULL | NULL   |
|    14 | Lu Wushuang   |  17 | F      |       3 |      NULL | NULL | NULL | NULL | NULL   |
|    15 | Duan Yu       |  19 | M      |       4 |      NULL | NULL | NULL | NULL | NULL   |
|    16 | Xu Zhu        |  21 | M      |       1 |      NULL | NULL | NULL | NULL | NULL   |
|    17 | Lin Chong     |  25 | M      |       4 |      NULL | NULL | NULL | NULL | NULL   |
|    18 | Hua Rong      |  23 | M      |       7 |      NULL | NULL | NULL | NULL | NULL   |
|    19 | Xue Baochai   |  18 | F      |       6 |      NULL | NULL | NULL | NULL | NULL   |
|    20 | Diao Chan     |  19 | F      |       7 |      NULL | NULL | NULL | NULL | NULL   |
|    21 | Huang Yueying |  22 | F      |       6 |      NULL | NULL | NULL | NULL | NULL   |
|    22 | Xiao Qiao     |  20 | F      |       1 |      NULL | NULL | NULL | NULL | NULL   |
|    23 | Ma Chao       |  23 | M      |       4 |      NULL | NULL | NULL | NULL | NULL   |
|    24 | Xu Xian       |  27 | M      |    NULL |      NULL | NULL | NULL | NULL | NULL   |
|    25 | Sun Dasheng   | 100 | M      |    NULL |      NULL | NULL | NULL | NULL | NULL   |
+-------+---------------+-----+--------+---------+-----------+------+------+------+--------+
25 rows in set (0.00 sec)

**#先左外连接，再过滤**
MariaDB [hellodb]> select * from students s left outer join teachers t on s.teacherid=t.tid where s.teacherid is null;
+-------+---------------+-----+--------+---------+-----------+------+------+------+--------+
| StuID | Name          | Age | Gender | ClassID | TeacherID | TID  | Name | Age  | Gender |
+-------+---------------+-----+--------+---------+-----------+------+------+------+--------+
|     6 | Shi Qing      |  46 | M      |       5 |      NULL | NULL | NULL | NULL | NULL   |
|     7 | Xi Ren        |  19 | F      |       3 |      NULL | NULL | NULL | NULL | NULL   |
|     8 | Lin Daiyu     |  17 | F      |       7 |      NULL | NULL | NULL | NULL | NULL   |
|     9 | Ren Yingying  |  20 | F      |       6 |      NULL | NULL | NULL | NULL | NULL   |
|    10 | Yue Lingshan  |  19 | F      |       3 |      NULL | NULL | NULL | NULL | NULL   |
|    11 | Yuan Chengzhi |  23 | M      |       6 |      NULL | NULL | NULL | NULL | NULL   |
|    12 | Wen Qingqing  |  19 | F      |       1 |      NULL | NULL | NULL | NULL | NULL   |
|    13 | Tian Boguang  |  33 | M      |       2 |      NULL | NULL | NULL | NULL | NULL   |
|    14 | Lu Wushuang   |  17 | F      |       3 |      NULL | NULL | NULL | NULL | NULL   |
|    15 | Duan Yu       |  19 | M      |       4 |      NULL | NULL | NULL | NULL | NULL   |
|    16 | Xu Zhu        |  21 | M      |       1 |      NULL | NULL | NULL | NULL | NULL   |
|    17 | Lin Chong     |  25 | M      |       4 |      NULL | NULL | NULL | NULL | NULL   |
|    18 | Hua Rong      |  23 | M      |       7 |      NULL | NULL | NULL | NULL | NULL   |
|    19 | Xue Baochai   |  18 | F      |       6 |      NULL | NULL | NULL | NULL | NULL   |
|    20 | Diao Chan     |  19 | F      |       7 |      NULL | NULL | NULL | NULL | NULL   |
|    21 | Huang Yueying |  22 | F      |       6 |      NULL | NULL | NULL | NULL | NULL   |
|    22 | Xiao Qiao     |  20 | F      |       1 |      NULL | NULL | NULL | NULL | NULL   |
|    23 | Ma Chao       |  23 | M      |       4 |      NULL | NULL | NULL | NULL | NULL   |
|    24 | Xu Xian       |  27 | M      |    NULL |      NULL | NULL | NULL | NULL | NULL   |
|    25 | Sun Dasheng   | 100 | M      |    NULL |      NULL | NULL | NULL | NULL | NULL   |
+-------+---------------+-----+--------+---------+-----------+------+------+------+--------+
20 rows in set (0.00 sec)

#右外连接
MariaDB [hellodb]> select * from students s right outer join teachers t on s.teacherid=t.tid ;
+-------+-------------+------+--------+---------+-----------+-----+---------------+-----+--------+
| StuID | Name        | Age  | Gender | ClassID | TeacherID | TID | Name          | Age | Gender |
+-------+-------------+------+--------+---------+-----------+-----+---------------+-----+--------+
|     1 | Shi Zhongyu |   22 | M      |       2 |         3 |   3 | Miejue Shitai |  77 | F      |
|     4 | Ding Dian   |   32 | M      |       4 |         4 |   4 | Lin Chaoying  |  93 | F      |
|     5 | Yu Yutong   |   26 | M      |       3 |         1 |   1 | Song Jiang    |  45 | M      |
|  NULL | NULL        | NULL | NULL   |    NULL |      NULL |   2 | Zhang Sanfeng |  94 | M      |
+-------+-------------+------+--------+---------+-----------+-----+---------------+-----+--------+
4 rows in set (0.00 sec)

**#右外连接的扩展用法**
MariaDB [hellodb]> select * from students s right outer join teachers t on s.teacherid=t.tid where s.teacherid is null;
+-------+------+------+--------+---------+-----------+-----+---------------+-----+--------+
| StuID | Name | Age  | Gender | ClassID | TeacherID | TID | Name          | Age | Gender |
+-------+------+------+--------+---------+-----------+-----+---------------+-----+--------+
|  NULL | NULL | NULL | NULL   |    NULL |      NULL |   2 | Zhang Sanfeng |  94 | M      |
+-------+------+------+--------+---------+-----------+-----+---------------+-----+--------+

****#完全外连接 full outer joion**
MariaDB [hellodb]> select s.stuid,s.name,s.age,t.tid,t.name,t.age from students as s left join teachers as t on s.teacherid=t.tid union  select s.stuid,s.name,s.age,t.tid,t.name,t.age from students as s right join teachers as t on s.teacherid=t.tid;
+-------+---------------+------+------+---------------+------+
| stuid | name          | age  | tid  | name          | age  |
+-------+---------------+------+------+---------------+------+
|     1 | Shi Zhongyu   |   22 |    3 | Miejue Shitai |   77 |
|     2 | Shi Potian    |   22 | NULL | NULL          | NULL |
|     3 | Xie Yanke     |   53 | NULL | NULL          | NULL |
|     4 | Ding Dian     |   32 |    4 | Lin Chaoying  |   93 |
|     5 | Yu Yutong     |   26 |    1 | Song Jiang    |   45 |
|     6 | Shi Qing      |   46 | NULL | NULL          | NULL |
|     7 | Xi Ren        |   19 | NULL | NULL          | NULL |
|     8 | Lin Daiyu     |   17 | NULL | NULL          | NULL |
|     9 | Ren Yingying  |   20 | NULL | NULL          | NULL |
|    10 | Yue Lingshan  |   19 | NULL | NULL          | NULL |
|    11 | Yuan Chengzhi |   23 | NULL | NULL          | NULL |
|    12 | Wen Qingqing  |   19 | NULL | NULL          | NULL |
|    13 | Tian Boguang  |   33 | NULL | NULL          | NULL |
|    14 | Lu Wushuang   |   17 | NULL | NULL          | NULL |
|    15 | Duan Yu       |   19 | NULL | NULL          | NULL |
|    16 | Xu Zhu        |   21 | NULL | NULL          | NULL |
|    17 | Lin Chong     |   25 | NULL | NULL          | NULL |
|    18 | Hua Rong      |   23 | NULL | NULL          | NULL |
|    19 | Xue Baochai   |   18 | NULL | NULL          | NULL |
|    20 | Diao Chan     |   19 | NULL | NULL          | NULL |
|    21 | Huang Yueying |   22 | NULL | NULL          | NULL |
|    22 | Xiao Qiao     |   20 | NULL | NULL          | NULL |
|    23 | Ma Chao       |   23 | NULL | NULL          | NULL |
|    24 | Xu Xian       |   27 | NULL | NULL          | NULL |
|    25 | Sun Dasheng   |  100 | NULL | NULL          | NULL |

**#自连接**
MariaDB [hellodb]> select * from emp;
+------+----------+----------+
| id | name | leaderid |
+------+----------+----------+
| 1 | mage | NULL |
| 2 | zhangsir | 1 |
| 3 | wang | 2 |
| 4 | zhang | 3 |
+------+----------+----------+
4 rows in set (0.00 sec)
MariaDB [hellodb]> select e.name,l.name from emp as e inner join emp as l on
e.leaderid=l.id;
+----------+----------+
| name | name |
+----------+----------+
| zhangsir | mage |
| wang | zhangsir |
| zhang | wang |
+----------+----------+
3 rows in set (0.00 sec)

**#三张表连接示例**
MariaDB [hellodb]> select st.name,co.course,sc.score from students st inner join scores sc on st.stuid=sc.stuid inner join courses co on sc.courseid=co.CourseID;
+-------------+----------------+-------+
| name        | course         | score |
+-------------+----------------+-------+
| Shi Zhongyu | Kuihua Baodian |    77 |
| Shi Zhongyu | Weituo Zhang   |    93 |
| Shi Potian  | Kuihua Baodian |    47 |
| Shi Potian  | Daiyu Zanghua  |    97 |
| Xie Yanke   | Kuihua Baodian |    88 |
| Xie Yanke   | Weituo Zhang   |    75 |
| Ding Dian   | Daiyu Zanghua  |    71 |
| Ding Dian   | Kuihua Baodian |    89 |
| Yu Yutong   | Hamo Gong      |    39 |
| Yu Yutong   | Dagou Bangfa   |    63 |
| Shi Qing    | Hamo Gong      |    96 |
| Xi Ren      | Hamo Gong      |    86 |
| Xi Ren      | Dagou Bangfa   |    83 |
| Lin Daiyu   | Taiji Quan     |    57 |
| Lin Daiyu   | Jinshe Jianfa  |    93 |
+-------------+----------------+-------+

SELECT语句处理的顺序

在这里插入图片描述
查询执行路径中的组件：查询缓存、解析器、预处理器、优化器、查询执行引擎、存储引擎
SELECT语句的执行流程：

	FROM Clause --> WHERE Clause --> GROUP BY --> HAVING Clause -->SELECT --> ORDER
BY --> LIMIT

1.3.3.3 SQL注入

#SQL 注入
select * from user where name='admin' and password='' or '1'='1';
select * from user where name='admin' and password='' or '1=1';
select * from user where name='admin'; -- ' and password='magedu123';

1.3.4 DCL：Data Control Language 数据控制语言

	GRANT，REVOKE，COMMIT，ROLLBACK

1.3.4 .1 授权命令GRANT

1.语法：

GRANT priv_type [(column_list)],... ON [object_type] priv_level TO 'user'@'host'
[IDENTIFIED BY 'password'] [WITH GRANT OPTION];
priv_type: ALL [PRIVILEGES]
object_type:TABLE | FUNCTION | PROCEDURE
priv_level: *(所有库) |*.* | db_name.* | db_name.tbl_name | tbl_name(当前库
的表) | db_name.routine_name(指定库的函数,存储过程,触发器)
with_option: GRANT OPTION
| MAX_QUERIES_PER_HOUR count
| MAX_UPDATES_PER_HOUR count
| MAX_CONNECTIONS_PER_HOUR count
| MAX_USER_CONNECTIONS count

范例：

GRANT SELECT (col1), INSERT (col1,col2) ON mydb.mytbl TO 'someuser'@'somehost‘;
GRANT ALL ON wordpress.* TO wordpress@'192.168.8.%' IDENTIFIED BY 'magedu';
GRANT ALL PRIVILEGES ON *.* TO 'root'@'192.168.8.%' IDENTIFIED BY 'magedu' WITH GRANT OPTION;

参考：https://dev.mysql.com/doc/refman/5.7/en/grant.html

1.3.4 .2 取消授权：REVOKE

1.语法

REVOKE priv_type [(column_list)] [, priv_type [(column_list)]] ... ON
[object_type] priv_level FROM user [, user] ...

2.范例

REVOKE DELETE ON testdb.* FROM 'testuser'@‘172.16.0.%’;

参考：https://dev.mysql.com/doc/refman/5.7/en/revoke.html

3.查看指定用户获得的授权
#获取帮助 Help SHOW GRANTS
#指定用户授权 SHOW GRANTS FOR 'user'@'host';
#当前用户授权信息 SHOW GRANTS FOR CURRENT_USER[()];

注意：MariaDB服务进程启动时会读取mysql库中所有授权表至内存
(1) GRANT或REVOKE等执行权限操作会保存于系统表中，MariaDB的服务进程通常会自动重读授权表，使之生效
(2) 对于不能够或不能及时重读授权表的命令，可手动让MariaDB的服务进程重读授权表：mysql>FLUSH PRIVILEGES;

1.3.4 .3 COMMIT 提交

事务管理有相关内容

1.3.4 .4 ROLLBACK 回滚

同上

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