mysql -DML数据操纵语言（草稿）

select : 查询表中数据
insert : 向表中插入新数据
update : 更新表中数据
delete : 删除表中数据

*********mysql没有撤销，没有撤销，没有撤销**********

#创建库
CREATE DATABASE exercise;

#使用库
USE exercise;

#删除库
DROP exercise;

#创建列表
CREATE TABLE student
(sld VARCHAR(4) NOT NULL,
sname VARCHAR(8),
sage DATE,
ssex VARCHAR(4)
);

CREATE TABLE course
(cld VARCHAR(4),
cname VARCHAR(8),
tid VARCHAR(8));

CREATE TABLE teacher
(tid VARCHAR(4),
tname VARCHAR(16));

CREATE TABLE sc
(sld CHAR(8),
cld CHAR(16),
score INT);

#添加student表内数据
INSERT INTO student VALUES('s1','找1','1990-9-1','男');
INSERT INTO student VALUES('s2','钱2','1992-1-2','男');
INSERT INTO student VALUES('s3','孙3','1991-2-3','女');
INSERT INTO student VALUES('s4','李4','1991-3-3','女');
INSERT INTO student VALUES('s5','周5','1994-2-1','男');

#更新表中数据



#查看是否添加数据成功
SELECT * FROM student;

#添加course表内数据
INSERT INTO course VALUES('c1','python','t1');
INSERT INTO course VALUES('c2','java','t2');
INSERT INTO course VALUES('c3','cpp','t3');
INSERT INTO course VALUES('c4','c#','t4');

#查看是否成功成功添加数据数据
SELECT * FROM course;

#添加teacher表内数据
INSERT INTO teacher VALUES('t1','齐桓公');
INSERT INTO teacher VALUES('t2','秦穆公');
INSERT INTO teacher VALUES('t3','楚庄王');
INSERT INTO teacher VALUES('t4','夫差');

SELECT * FROM teacher;
DROP TABLE teacher;
#添加sc表内数据
INSERT INTO sc VALUES('s1','c1','59');
INSERT INTO sc VALUES('s1','c2','61');
INSERT INTO sc VALUES('s1','c3','99');
INSERT INTO sc VALUES('s1','c4','100');
INSERT INTO sc VALUES('s2','c1','99');
INSERT INTO sc VALUES('s2','c2','58');
INSERT INTO sc VALUES('s2','c3','100');
INSERT INTO sc VALUES('s2','c4','62');
INSERT INTO sc VALUES('s3','c1','18');
INSERT INTO sc VALUES('s3','c2','91');
INSERT INTO sc VALUES('s3','c3','45');
INSERT INTO sc VALUES('s3','c4','12');
INSERT INTO sc VALUES('s4','c1','89');
INSERT INTO sc VALUES('s4','c2','78');
INSERT INTO sc VALUES('s4','c3','59');
INSERT INTO sc VALUES('s4','c4','99');

#查看数据是否添加成功,模糊查询是否有遗漏

SELECT * FROM sc
WHERE sld LIKE 's1';

SELECT * FROM sc
WHERE sld LIKE 's2';


SELECT * FROM sc
WHERE sld LIKE 's3';


SELECT * FROM sc
WHERE sld LIKE 's4';

#一. 插入语句
/*
#方式一：经典插入
语法：
	insert into 表名（列名，...） values(值1，...)
	#1.插入的值的类型要与列的类型一致或兼容
INSERT INTO 
#2.不可以null的列必须插入值，可以为null的列要么列名写着值为空，要么列名直接不写

#3.列的顺序可以调换，列数和值的个数必须一致

#4.可以省略列名字，默认所有列，而且烈的顺序和表中列的顺序一致

#方式二：
语法：
	insert into 表名
	set 列名=值，列名=值....

***方式一支持插入多行，方式二只支持插入单行

*/

#eg1:方式一 - 插入完整行
INSERT INTO student(sld,sname,sage,ssex) VALUES('s32','ta1','1999-12-1','male');
INSERT INTO student VALUES('s12','tom','199-1-2','male');

#eg2:方式一 - 插入部分行
INSERT INTO student(sld,sname) VALUES('s21','sa');

#eg3:方式一 - 插入多行
INSERT INTO student VALUES('s21','t2m','199-2-2','male'),('s34','tam','1999-10-1','male');

#eg4:方式一 - 插入检索出来的语句
INSERT INTO student(sld) SELECT sld FROM sc;

#eg5:方式二 -
INSERT INTO student SET sld='s212';



#二 更新语句

/*
***进行列的更新
1.修改单表语句★
语法：
	update 表名                   1
	set 列=新值...
	where 筛选条件；              2
2.修改多表语句
语法：
	update 表1 inner join 表2 on 连接条件
	sete 列=值，列=值
	where 筛选条件；

***更新数据不要省略where，否则会更新所有行
*/

#1.单表更新
UPDATE student
SET sld='s100'
WHERE sname LIKE '%m';


#三.删除语句
/*
***删除行
方式一：delete
语法：
单表删除
	delete from 表名 where
	
多表删除：
	delete  表1别名，表2别名
	from 表1别名 inner jion 表2别名 on 连接条件
	where 筛选条件
方式二：清空数据
	trunct table 表名；
	
方式一与方式二的区别：
	1.delete 后可以加where条件，truncate后不能加
	2.truncate相当于清空条件
	3.假如删除表中有自增长列
	  delete删除后插入时，从断点值开始
	  truncate从1开始
	
*/
#eg:单表删除 
DELETE FROM student WHERE sld='s1';

#eg:清空表
TRUNCATE TABLE sc;


#一 基础查询

#eg1:查询单个字段
SELECT sld FROM sc;

#eg2:查询多个字段
SELECT sage,sld FROM student;

#eg3:拼接查询
SELECT CONCAT(sage,sld) FROM student;

#eg4:去重查询
SELECT DISTINCT(sld) FROM sc;


#一 条件查询
#注：可使用逻辑表达式连接条件（and ， not ，or）

#条件查询1-条件表达式（< = > >= <= != ）

#eg5:查询有课程达到满分的学生编号
SELECT DISTINCT(sld) 
FROM sc
WHERE score=100;

#eg6：查询有课程不及格学生的编号
SELECT sld
FROM sc
WHERE NOT score>=60;

#eg7：查询c1课程在60到80内的学生的编号
SELECT * 
FROM sc
WHERE score<=80 AND score>=60;


#条件查询2-模糊查询（like,between and,in,is null）

#eg8:查询姓秦的老师编号 
SELECT tid
FROM teacher
WHERE tname LIKE '秦%';

#eg9:查询有课程及格学生的编号
SELECT * 
FROM sc
WHERE score BETWEEN 60 AND 100;

#eg10:查询分数为空的学生编号的学生  
SELECT * 
FROM sc
WHERE score IS NULL;


SELECT * 
FROM sc
WHERE score IS NOT NULL;

#eg11：查询姓带有公的老师编号

SELECT tid
FROM teacher
WHERE tname LIKE '%公' OR tname LIKE '公%';

#注:"\%"和'\_'序列用于搜索可能解释为通配符的模式匹配环境中的%和_文字实例
SELECT * FROM employees WHERE last_name LIKE 'K\_%';

# 日期型数字
#eg14:查询出生年月在1990到1992的学生编号
SELECT *
FROM student
WHERE sage>('1900-1-1')AND sage<('1999-1-1');


# in的用法 - in里面放查询条件(不是查询范围）

SELECT *
FROM employees
WHERE department_id IN (30,50,100);

#三 排序查询

#升序查询
SELECT salary,employee_id
FROM employees
WHERE salary BETWEEN 5000 AND 50000
ORDER BY salary ASC;

#降序查询
SELECT salry,employee_id
FROM employees
WHERE NOT salary<10000
ORDER BY employee_id DESC;

#四 函数

#字符函数1-length():获取参数值的字节数
SELECT LENGTH(first_name) FROM employees;

#字符函数2-concat():拼接字符
SELECT CONCAT(first_name,last_name) FROM employees;

#字符函数3-upper,lower:改变大小写

SELECT LOWER(first_name),UPPER(last_name) FROM employees;

SELECT * FROM employees;

#字符函数4-substr(s,n,len):返回字符串s从第n个字符长度(索引，sql语言索引从1开始)为len的子字符串

SELECT SUBSTR(first_name,3,2) FROM employees; 
SELECT SUBSTR(first_name,3) FROM employees; 
#eg
SELECT CONCAT(SUBSTR(first_name,3),'_',SUBSTR(last_name,3)) FROM employees; 

#字符函数5-instr(s,sl)  返回子字符串在主字符串中第一次出现的索引，找不到返回0

SELECT INSTR(first_name,'K') FROM employees;

#字符函数6-replace(s,s1,s2)  在主字符串中用s2子字符串替代s1子字符串
#***错误语句：SELECT replace(first_name,Lex,lex)  FROM employees;
SELECT REPLACE(first_name,'Lex','lex')  FROM employees;

#字符函数7-trim(s) -去字符，默认去空格
#          trim(a from s) - 去掉指定字符

SELECT TRIM(first_name)  FROM employees;
SELECT TRIM('L' FROM first_name)  FROM employees;

#字符函数 - lpad(s,2,'*')  -左填充函数，用指定字符实现左填充指定长度，若填充数少于字符数则返回填充长度的字符数

SELECT LPAD(first_name,10,'*')  FROM employees;
SELECT LPAD(first_name,2,'*')  FROM employees;

#字符函数9 - rpad() -右填充函数，作用同右填充

SELECT RPAD(first_name,10,'*')  FROM employees;
SELECT RPAD(first_name,2,'*')  FROM employees;

#填充函数填充长度少于字节长度时，都是从左到右返回填充长度的字符数


#数学函数1-round(x,d):四舍五入

SELECT ROUND(salary) FROM employees;
SELECT ROUND(salary/1000,2) FROM employees;

#数学函数2-mode(x,m):取余(m为被除数)

SELECT MOD(salary,1000) FROM employees; 

#数学函数3-ceil(x):向上取整
SELECT CEIL(salary%1000) FROM employees;

#数学函数4-floor(x):向下取整
SELECT FLOOR(salary%1000) FROM employees;

SELECT * FROM employees;

#数学函数5-truncate(x,d):截断函数-小数点后保留d位
SELECT TRUNCATE(phone_number,4) FROM employees;

#日期函数1-查询现在时间datetime(),curdate,curtime()
SELECT NOW();

SELECT CURDATE();

SELECT CURTIME();

#日期函数2-将字符转换为指定格式的日期
SELECT DATE_FORMAT(NOW(),'%Y-%m-%d %H:%i:%s') AS now_time;

#分组函数：max，min，sum，avg，count
SELECT MAX(salary),MIN(salary),COUNT(salary),AVG(salary),SUM(salary) FROM employees;

#五 分组查询

#1 简单分组查询 - 查询每个工种的平均工资
SELECT job_id,AVG(salary) FROM employees GROUP BY job_id;

#2 分组前筛选 - 查询工资邮箱中包含a的各个部门的平均工资

SELECT department_id,AVG(salary) FROM employees WHERE email LIKE '%a%' GROUP BY department_id;

#3 分组后筛选 - 查询哪个部门的员工数＞2，并对结果进行升序排序

SELECT department_id,COUNT(*) 
FROM employees  
GROUP BY department_id 
HAVING COUNT(*)>2 
ORDER BY COUNT(*) ASC;

#4 多条件筛选查询 - 查询每个部门，每个工种的平均工资
SELECT department_id,job_id,AVG(salary)
FROM employees
GROUP BY department_id,job_id
ORDER BY department_id ASC;

#count(*):返回检索行的数目，不论是否包含NULL值，

#六 连接查询 - 查询的字段来自多个表时
/*
sql199语法：
	select 查询列表
	from 表1 别名 
	[连接类型] join 表2 on 连接条件
	where 筛选条件
	grouup by
	having 筛选条件
	order by 排序列表	
*/

#1 内连接 - 返回交集

SELECT 查询列表
FROM 表 1
INNER JOIN  表2 ON 连接条件

#1.1等值连接  

#eg1.查询员工名和部门名

SELECT first_name,department_name 
FROM employees AS e INNER
JOIN departments AS d
ON e.`department_id`=d.`department_id`;

#eg2.查询名字中包含e的员工名和工种名

SELECT first_name,job_title 
FROM employees AS e INNER
JOIN jobs AS j
ON e.`job_id`=j.`job_id`
WHERE first_name LIKE '%e%';

#eg3.查询部门个数>3的城市名及部门个数

SELECT city,COUNT(*) 
FROM departments AS d INNER
JOIN locations AS l
ON d.`location_id` = l.`location_id`
GROUP BY city
HAVING COUNT(*)>3;

#eg4.三表连接 - 查询员工名，部门名，工种名，并按部门人数进行排序

SELECT first_name,department_name,job_title
FROM employees AS e 
INNER JOIN departments AS d
ON e.`department_id` = d.`department_id`
INNER JOIN jobs AS j 
ON e.`job_id` = j.`job_id`;

SELECT first_name,department_name,job_title
FROM departments AS d
INNER JOIN employees AS e ON d.`department_id`=e.`department_id`
INNER JOIN jobs AS j ON e.`job_id` =j.`job_id`;

#多表查询与表的链接顺序无关


#1.2 内连接 - 非等值连接

#eg：查询员工工资级别
SELECT *
FROM 表1
INNER JOIN 表2
ON 表1.列名 BETWEEN 表2.列名 AND 表2.列名2

#1.3 内连接 - 自连接

SELECT e.first_name 
FROM employees AS e
INNER JOIN  employees AS p ON e.`department_id`=p.`department_id`;

#制定多个键时，可以使用and，or连接条件
#规范语法：使用连接时select子句中按照“表别名.列名”格式书写。

#2 外连接 

#外连接分主从表，左外连接左边为主表，右外连接右边为主表，左外和右外交换两个表的顺序可以实现同样的结果。
#

#2.1 左外连接 - 返回左边表中的所有行和右边表中与之相匹配的列值，若右表没有则用NULL代替

SELECT *
FROM employees AS e
LEFT JOIN departments AS d
ON e.`department_id`=d.`department_id`;

SELECT *
FROM departments AS d
LEFT JOIN employees AS e
ON e.`department_id`=d.`department_id`;

#2.2右外连接

SELECT *
FROM employees AS e
RIGHT JOIN departments AS d
ON e.`department_id`=d.`department_id`

#2.3全外连接 - 返回左右两表的全部行 - mysql不支持需要用union把左右外连接在一起

SELECT *
FROM employees AS e
RIGHT JOIN departments AS d
ON e.`department_id`=d.`department_id`
UNION
SELECT *
FROM employees AS e
LEFT JOIN departments AS d
ON e.`department_id`=d.`department_id`;


#3 交叉连接 - 笛卡尔积

SELECT *
FROM departments
CROSS JOIN  employees;


#七 子查询 
/*
1.定义：
	出现在其他语句的elect语句，被称为子查询或内查询，u要放在括号内
	
2.特定：
	1.子查询以视图为基础，是一张一次性视图。
	2.子查询放在括号内；
	3.子查询的执行优先于主查询；
	4.标量子查询一般配合单行操作符号使用<> = <= >=
	  列子查询一般搭配多行操作符使用。
	  
3.分类：
	标量子查询：返回一行一列的结果集
	行子查询：返回一行一列的结果集
	列子查询：返回一列多行的结果集
	表子查询：返回多行多列的结果集
4.位置：
	select后面 仅仅支持标量子查询
	from后面 支持表子查询
	where或having后面 标量子查询，列子查询，行子查询
*/

#一 where 或 having后面

#1.标量子查询

#eg1 标量子查询 查询谁的工资比Lex的高

SELECT first_name,salary
FROM employees
WHERE salary > (SELECT salary 
		FROM employees
		WHERE first_name LIKE 'Den');


#eg2.标量子查询 - 返回job_id与141号员工相同，salary比143号多的员工，查询员工姓名
SELECT CONCAT(last_name,first_name)
FROM employees 
WHERE job_id = (SELECT job_id FROM employees WHERE employee_id=141) 
	AND salary>(SELECT salary FROM employees WHERE employee_id=143)


#eg3：标量子查询 - 返回公司工资最少的员工last_name,job_id和salary

SELECT last_name,job_id,salary
FROM employees
WHERE salary = (SELECT MIN(salary) FROM employees);

#eg4：标量子查询 - 查询最低工资>50号部门最低工资的部门id,及其最低工资
SELECT department_id,MIN(salary)
FROM employees
GROUP BY department_id
HAVING MIN(salary) > (SELECT MIN(salary) FROM employees WHERE department_id=50);


#2.列子查询

/*
多行操作符 in/not in（等于） 
any/some =max（和子查询返回的某一个查询） 
all =min（和查询的值全部比较）
*/

#eg1:返回location id是1400或1700的部门的所有员工姓名
SELECT CONCAT(last_name,first_name)
FROM employees
WHERE department_id IN(SELECT DISTINCT(department_id) FROM departments WHERE location_id IN(1400,1700));

#eg2:返回其他部门中比job_id为'IT——PROG'部门所有工资低的员工的员工号，姓名，job_id,salary
SELECT employee_id,first_name,job_id,salary
FROM employees
WHERE salary < ANY(SELECT DISTINCT(salary) FROM employees WHERE job_id='IT_PROG') AND job_id<>'IT_PROG';

#3 行子查询
#eg:查询员工编号最小的并且要求工资最高的员工信息
SELECT *
FROM employees
WHERE employee_id = ALL(SELECT MIN(employee_id) FROM employees) 
	AND salary = ANY(SELECT MAX(salary) FROM employees); 

#二 select后面 - 查询和统计并存(返回值)
#eg:查询每个部门的信息及员工个数

#错误代码
SELECT *,(SELECT COUNT(*) FROM employees GROUP BY department_id)
FROM departments;


 SELECT d.*,
  (SELECT COUNT(*)
  FROM employees e
  WHERE d.`department_id` = e.department_id
 )
FROM departments d;

#三 from后面-将查询结果充当一张表，必须起别名
#eg:查询每个部门的平均工资的工资等级




#四 相关子查询 - 是否存在，子查询用到了主查询的信息，子查询的结果是否有值。
#查询员工的部门名
SELECT department_name
FROM departments d
WHERE EXISTS(
	SELECT *
	FROM employees e
	WHERE d.`department_id`=e.`department_id`);





#八 union查询 - 将多条查询语句的结果合并成一个结果
/*
应用场景：查询的结果来自多个表，且多个表没有直接的连接关系，但查询的部分有一定关系

特点：要求多条查询语句的查询列数
      要求多条查询语句的每一列类型和顺序最好一致
      联合查询会自动去重，不想去重加union all
*/
#引入案例：查询部门编号>90或邮箱包含a的员工信息

SELECT * FROM employees WHERE department_id>90 OR email LIKE '%a%';

SELECT * FROM employees WHERE email LIKE '%a%'
UNION #all
SELECT * FROM employees WHERE department_id>90;