MySQL简单查询和单表查询

MySQL记录操作

概览

MySQL数据操作： DML

在MySQL管理软件中，可以通过SQL语句中的DML语言来实现数据的操作，包括

使用INSERT实现数据的插入
UPDATE实现数据的更新
使用DELETE实现数据的删除
使用SELECT查询数据以及。

插入数据insert

1. 插入完整数据（顺序插入）

    语法一：

    INSERT INTO 表名(字段1,字段2,字段3…字段n) VALUES(值1,值2,值3…值n);

    语法二：

    INSERT INTO 表名 VALUES (值1,值2,值3…值n);

2. 指定字段插入数据

    语法：

    INSERT INTO 表名(字段1,字段2,字段3…) VALUES (值1,值2,值3…);

3. 插入多条记录

    语法：

    INSERT INTO 表名 VALUES

        (值1,值2,值3…值n),

        (值1,值2,值3…值n),

        (值1,值2,值3…值n);

4. 插入查询结果

    语法：

    INSERT INTO 表名(字段1,字段2,字段3…字段n)

                    SELECT (字段1,字段2,字段3…字段n) FROM 表2

                    WHERE …;

更新数据update

语法：

    UPDATE 表名 SET

        字段1=值1,

        字段2=值2,

        WHERE CONDITION;

示例：

    UPDATE mysql.user SET password=password(‘123’)

        where user=’root’ and host=’localhost’;

删除数据delete

语法：

    DELETE FROM 表名

        WHERE CONITION;

示例：

    DELETE FROM mysql.user

        WHERE password=’’;

练习：

    更新MySQL root用户密码为mysql123

    删除除从本地登录的root用户以外的所有用户

查询数据 search

1.单表查询

关键字执行的优先级:

from

where

group by

select

distinct

having

order by

limit

1.找到表:from

2.拿着where指定的约束条件，去文件/表中取出一条条记录

3.将取出的一条条记录进行分组group by，如果没有group by，则整体作为一组

4.执行select（去重）

5.将分组的结果进行having过滤

6.将结果按条件排序：order by

7.限制结果的显示条数

简单查询

#创建表

create table employee(

id int not null unique auto_increment,

emp_name varchar(20) not null,

sex enum('male','female') not null default 'male', #大部分是男的

age int(3) unsigned not null default 28,

hire_date date not null,

post varchar(50),

post_comment varchar(100),

salary double(15,2),

office int, #一个部门一个屋子

depart_id int

);

#查看表结构

mysql> desc employee;

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

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

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

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

| emp_name     | varchar(20)           | NO   |     | NULL    |                |

| sex          | enum('male','female') | NO   |     | male    |                |

| age          | int(3) unsigned       | NO   |     | 28      |                |

| hire_date    | date                  | NO   |     | NULL    |                |

| post         | varchar(50)           | YES  |     | NULL    |                |

| post_comment | varchar(100)          | YES  |     | NULL    |                |

| salary       | double(15,2)          | YES  |     | NULL    |                |

| office       | int(11)               | YES  |     | NULL    |                |

| depart_id    | int(11)               | YES  |     | NULL    |                |

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

#插入记录

#三个部门：教学，销售，运营

insert into employee(emp_name,sex,age,hire_date,post,salary,office,depart_id) values

('egon','male',18,'20170301','办事处',7300.33,401,1), #以下是教学部

('anwen','male',78,'20150302','teacher',1000000.31,401,1),

('wudi','male',81,'20130305','teacher',8300,401,1),

('yuanhao','male',73,'20140701','teacher',3500,401,1),

('liwen','male',28,'20121101','teacher',2100,401,1),

('jingliyang','female',18,'20110211','teacher',9000,401,1),

('jinxin','male',18,'19000301','teacher',30000,401,1),

('成龙','male',48,'20101111','teacher',10000,401,1),

('歪歪','female',48,'20150311','sale',3000.13,402,2),#以下是销售部门

('丫丫','female',38,'20101101','sale',2000.35,402,2),

('丁丁','female',18,'20110312','sale',1000.37,402,2),

('星星','female',18,'20160513','sale',3000.29,402,2),

('格格','female',28,'20170127','sale',4000.33,402,2),

('张xx','male',28,'20160311','operation',10000.13,403,3), #以下是运营部门

('程咬金','male',18,'19970312','operation',20000,403,3),

('程咬银','female',18,'20130311','operation',19000,403,3),

('程咬铜','male',18,'20150411','operation',18000,403,3),

('程咬铁','female',18,'20140512','operation',17000,403,3)

;

#ps：如果在windows系统中，插入中文字符，select的结果为空白，可以将所有字符编码统一设置成gbk

准备表和记录

#简单查询

    SELECT id,emp_name,sex,age,hire_date,post,post_comment,salary,office,depart_id

    FROM employee;

    SELECT * FROM employee;

    SELECT emp_name,salary FROM employee;

#避免重复DISTINCT

    SELECT DISTINCT post FROM employee;    

#通过四则运算查询

    SELECT emp_name, salary*12 FROM employee;

    SELECT emp_name, salary*12 AS Annual_salary FROM employee;

    SELECT emp_name, salary*12 Annual_salary FROM employee;

#定义显示格式

   CONCAT() 函数用于连接字符串

   SELECT CONCAT('姓名: ',emp_name,'  年薪: ', salary*12)  AS Annual_salary

   FROM employee;

   CONCAT_WS() 第一个参数为分隔符

   SELECT CONCAT_WS(':',emp_name,salary*12)  AS Annual_salary

   FROM employee;

   结合CASE语句：

   SELECT

       (

           CASE

           WHEN emp_name = 'jingliyang' THEN

               emp_name

           WHEN emp_name = 'alex' THEN

               CONCAT(emp_name,'_BIGSB')

           ELSE

               concat(emp_name, 'SB')

           END

       ) as new_name

   FROM

       employee;

小练习：

1 查出所有员工的名字，薪资,格式为

    <名字:egon>    <薪资:3000>

2 查出所有的岗位（去掉重复）

3 查出所有员工名字，以及他们的年薪,年薪的字段名为annual_year

select concat('<名字:',emp_name,'>    ','<薪资:',salary,'>') from employee;

select distinct depart_id from employee;

select emp_name,salary*12 annual_salary from employee;

where约束

where字句中可以使用：

比较运算符：> < >= <= <> !=
between 80 and 100 值在80到100之间
in(80,90,100) 值是80或90或100
like 'e%'

通配符可以是%或_，

%表示任意多字符

_表示一个字符
逻辑运算符：在多个条件直接可以使用逻辑运算符 and or not

#1:单条件查询

    SELECT emp_name FROM employee

        WHERE post='sale';

#2:多条件查询

    SELECT emp_name,salary FROM employee

        WHERE post='teacher' AND salary>10000;

#3:关键字BETWEEN AND

    SELECT emp_name,salary FROM employee

        WHERE salary BETWEEN 10000 AND 20000;

    SELECT emp_name,salary FROM employee

        WHERE salary NOT BETWEEN 10000 AND 20000;

#4:关键字IS NULL(判断某个字段是否为NULL不能用等号，需要用IS)

    SELECT emp_name,post_comment FROM employee

        WHERE post_comment IS NULL;

    SELECT emp_name,post_comment FROM employee

        WHERE post_comment IS NOT NULL;

    SELECT emp_name,post_comment FROM employee

        WHERE post_comment=''; 注意''是空字符串，不是null

    ps：

        执行

        update employee set post_comment='' where id=2;

        再用上条查看，就会有结果了

#5:关键字IN集合查询

    SELECT emp_name,salary FROM employee

        WHERE salary=3000 OR salary=3500 OR salary=4000 OR salary=9000 ;

    SELECT emp_name,salary FROM employee

        WHERE salary IN (3000,3500,4000,9000) ;

    SELECT emp_name,salary FROM employee

        WHERE salary NOT IN (3000,3500,4000,9000) ;

#6:关键字LIKE模糊查询

    通配符’%’

    SELECT * FROM employee

            WHERE emp_name LIKE 'eg%';

    通配符’_’

    SELECT * FROM employee

            WHERE emp_name LIKE 'al__';

小练习：

1. 查看岗位是teacher的员工姓名、年龄

2. 查看岗位是teacher且年龄大于30岁的员工姓名、年龄

3. 查看岗位是teacher且薪资在9000-1000范围内的员工姓名、年龄、薪资

4. 查看岗位描述不为NULL的员工信息

5. 查看岗位是teacher且薪资是10000或9000或30000的员工姓名、年龄、薪资

6. 查看岗位是teacher且薪资不是10000或9000或30000的员工姓名、年龄、薪资

7. 查看岗位是teacher且名字是jin开头的员工姓名、年薪

select emp_name,age from employee where post = 'teacher';

select emp_name,age from employee where post='teacher' and age > 30;

select emp_name,age,salary from employee where post='teacher' and salary between 9000 and 10000;

select * from employee where post_comment is not null;

select emp_name,age,salary from employee where post='teacher' and salary in (10000,9000,30000);

select emp_name,age,salary from employee where post='teacher' and salary not in (10000,9000,30000);

select emp_name,salary*12 from employee where post='teacher' and emp_name like 'jin%';

group by

单独使用GROUP BY关键字分组

    SELECT post FROM employee GROUP BY post;

    注意：我们按照post字段分组，那么select查询的字段只能是post，想要获取组内的其他相关信息，需要借助函数

GROUP BY关键字和GROUP_CONCAT()函数一起使用

    SELECT post,GROUP_CONCAT(emp_name) FROM employee GROUP BY post;#按照岗位分组，并查看组内成员名

    SELECT post,GROUP_CONCAT(emp_name) as emp_members FROM employee GROUP BY post;

GROUP BY与聚合函数一起使用

    select post,count(id) as count from employee group by post;#按照岗位分组，并查看每个组有多少人

强调：

如果我们用unique的字段作为分组的依据，则每一条记录自成一组，这种分组没有意义

多条记录之间的某个字段值相同，该字段通常用来作为分组的依据

聚合函数

#强调：聚合函数聚合的是组的内容，若是没有分组，则默认一组

示例：

    SELECT COUNT(*) FROM employee;

    SELECT COUNT(*) FROM employee WHERE depart_id=1;

    SELECT MAX(salary) FROM employee;

    SELECT MIN(salary) FROM employee;

    SELECT AVG(salary) FROM employee;

    SELECT SUM(salary) FROM employee;

    SELECT SUM(salary) FROM employee WHERE depart_id=3;

小练习：

1. 查询岗位名以及岗位包含的所有员工名字

2. 查询岗位名以及各岗位内包含的员工个数

3. 查询公司内男员工和女员工的个数

4. 查询岗位名以及各岗位的平均薪资

5. 查询岗位名以及各岗位的最高薪资

6. 查询岗位名以及各岗位的最低薪资

7. 查询男员工与男员工的平均薪资，女员工与女员工的平均薪资

#题1：分组

mysql> select post,group_concat(emp_name) from employee group by post;

#题目2：

mysql> select post,count(id) from employee group by post;

#题目3：

mysql> select sex,count(id) from employee group by sex;

#题目4：

mysql> select post,avg(salary) from employee group by post;

#题目5

mysql> select post,max(salary) from employee group by post;

#题目6

mysql> select post,min(salary) from employee group by post;

#题目七

mysql> select sex,avg(salary) from employee group by sex;

HAVING过滤

HAVING与WHERE不一样的地方在于!!!!!!

#！！！执行优先级从高到低：where > group by > having

#1. Where 发生在分组group by之前，因而Where中可以有任意字段，但是绝对不能使用聚合函数。

#2. Having发生在分组group by之后，因而Having中可以使用分组的字段，无法直接取到其他字段,可以使用聚合函数

select * from emp where salary > 100000;

mysql> select post,group_concat(emp_name) from emp group by post having salary > 10000;#错误，分组后无法直接取到salary字段

ERROR 1054 (42S22): Unknown column 'salary' in 'having clause'

mysql> select post,group_concat(emp_name) from emp group by post having avg(salary) > 10000;

小练习：

1. 查询各岗位内包含的员工个数小于2的岗位名、岗位内包含员工名字、个数

3. 查询各岗位平均薪资大于10000的岗位名、平均工资

4. 查询各岗位平均薪资大于10000且小于20000的岗位名、平均工资

select post,group_concat(emp_name),count(id) from employee group by post having count(id) < 2;

select post,avg(salary) from employee group by post having avg(salary) > 10000;

select post,avg(salary) from employee group by post having avg(salary) > 10000 and avg(salary) <20000;

ORDER BY 查询排序

按单列排序

    SELECT * FROM employee ORDER BY salary;

    SELECT * FROM employee ORDER BY salary ASC;

    SELECT * FROM employee ORDER BY salary DESC;

按多列排序:先按照age排序，如果年纪相同，则按照薪资排序

    SELECT * from employee

        ORDER BY age,

        salary DESC;

小练习：

1. 查询所有员工信息，先按照age升序排序，如果age相同则按照hire_date降序排序

2. 查询各岗位平均薪资大于10000的岗位名、平均工资,结果按平均薪资升序排列

3. 查询各岗位平均薪资大于10000的岗位名、平均工资,结果按平均薪资降序排列

select * from employee ORDER BY age asc,hire_date desc;

select post,avg(salary) from employee group by post having avg(salary) > 10000 order by avg(salary) asc;

select post,avg(salary) from employee group by post having avg(salary) > 10000 order by avg(salary) desc;

LIMIT 限制查询的记录数

示例：

    SELECT * FROM employee ORDER BY salary DESC

        LIMIT 3;                    #默认初始位置为0 

    SELECT * FROM employee ORDER BY salary DESC

        LIMIT 0,5; #从第0开始，即先查询出第一条，然后包含这一条在内往后查5条

    SELECT * FROM employee ORDER BY salary DESC

        LIMIT 5,5; #从第5开始，即先查询出第6条，然后包含这一条在内往后查5条

小练习：

select * from  employee limit 0,5;

select * from  employee limit 5,5;

select * from  employee limit 10,5;

使用正则表达式查询

SELECT * FROM employee WHERE emp_name REGEXP '^ale';

SELECT * FROM employee WHERE emp_name REGEXP 'on$';

SELECT * FROM employee WHERE emp_name REGEXP 'm{2}';

小结：对字符串匹配的方式

WHERE emp_name = 'egon';

WHERE emp_name LIKE 'yua%';

WHERE emp_name REGEXP 'on$';

巴特西

MySQL简单查询和单表查询

概览

插入数据insert

更新数据update

删除数据delete

查询数据 search

1.单表查询

关键字执行的优先级:

简单查询

where约束

group by

聚合函数

HAVING过滤

ORDER BY 查询排序

LIMIT 限制查询的记录数

使用正则表达式查询

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