sql 查询mysql 某张表的操作记录 mysql查询一个表

主要内容：

1.查询语法

2.关键字的执行优先级

3.简单查询

4.单条件查询

5.where 约束

6.分组查询： group by

7.使用聚合函数查询

8.having 过滤

9.查询排序：order by

10限制查询的记录数：limit

11.使用正则表达式查询

先建数据库（文件夹）、后表（文件）带字段，后记录（内容）。

company.employee
    员工id      id                  int             
    姓名        emp_name            varchar
    性别        sex                 enum
    年龄        age                 int
    入职日期     hire_date           date
    岗位        post                varchar
    职位描述     post_comment        varchar
    薪水        salary              double
    办公室       office              int
    部门编号     depart_id           int



#创建表
create table employee(
id int not null unique auto_increment,
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 |
| 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(name,sex,age,hire_date,post,salary,office,depart_id) values
('egon','male',18,'20170301','老男孩驻沙河办事处外交大使',7300.33,401,1), #以下是教学部
('alex','male',78,'20150302','teacher',1000000.31,401,1),
('wupeiqi','male',81,'20130305','teacher',8300,401,1),
('yuanhao','male',73,'20140701','teacher',3500,401,1),
('liwenzhou','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),

('张野','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)

一：查询语法：

select 字段1，字段2...  from  表名
             where  条件
             group by  field
             having   筛选
            order by field
            limit   限制条数

二：关键字的执行优先级（重点）

重点：关键字的优先级执行顺序
1.from
2.where
3.group by
4.having
5.select
6.distinct
7.order by
8.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.按照select后的字段得到一张新的虚拟表，如果有聚合函数，则将组内数据进行聚合

5.将4的结果过滤：having

6.查出结果：select

7.去重

8.将结果按条件排序：order by

9.限制结果的显示条数

三：简单查询

#简单查询
    select id,name,sex,age,hire_date,post,post_comment,salary,office,depart_id 
    from employee;

    select * from employee;

    select name,salary from employee;

#避免重复DISTINCT
    select distinct post from employee;    

#通过四则运算查询
    select name, salary*12 from employee;
    select name, salary*12 as Annual_salary from employee;
    select 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: ',name,'  年薪: ', salary*12)  AS Annual_salary 
   from employee;
   
   CONCAT_WS() 第一个参数为分隔符
   SELECT CONCAT_WS(':',name,salary*12)  AS Annual_salary 
   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：'，name,’> ' , '<薪资：',salary,'>') from employee;
select distinct depart_id from employee;
select name,salary*12 annual_salary from employee;

View Code

四：where  约束

强调： where是一种约束条件，mysql会拿着where指定的条件取表中取数据，而having则是在取出数据后进行过滤。

where字句中可以使用：

　　1.比较运算符： >< >= <= <> !=

　　2.between 80 and 100 值在 10 到 20 之间。

　　3.in （80,90,100)值是10 或 20 或 30.

　　4.like 'aray%' 

　　   patterm 可以是 %或_,

　　　%表示任意字符， _表示一个字符

　　5.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 name from employee where post = 'sale';

2.多条件查询
    select name,salary from employee where post='teacher' and salary>10000;

3.关键字查询：between and
    select name,salary from employee where salary between 10000 and 20000;
    select name,salary from employee where sal''ary not between 10000 and 20000;

4.关键字查询：is null（判断某个字段是否为null 不能用等号们需要用is）
    select name,post_comment from employee where post_comment is null;
    select name,post_comment from employee where post_comment is not null;
    select name,post_comment from employee where post_comment ='';  #注意：''是空字符串。
    ps:
        执行
        update employee set post_comment='' where  id=2;
        再用上条查看，就会有结果了。

5.关键字查询： in    
    select name,salary from employee where salary=3000 or salary=3500 or salary=4000;
    select name,salary from employee where salary  in (3000,3500,4000);
    select name,salary from employee where salary not in (3000,3500,4000);

6.关键字查询：like
    通配符 '%'
    select * from employee where name like 'ar%';

    通配符： '_'
    select * from employee where name like 'ar__';

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

1.
select name,age from employee where post ='teacher';

2.
select name,age from employee where post='teacher' and age>30;
''
3.
select name,age,salary from employee where post='teacher' and salary between 9000 adn 10000;

4.
select * from employee where post_comment is not null;

5.
select name,age,salary from employee where post='teacher' and salary  in(10000,9000,30000);

6.
select name,age,salary from employee where post='teacher' and salary not in(10000,9000,30000);

7.
select name,salary from empolyee where post='teacher' and name like 'jin%';

View Code

五：分组查询： group by

大前提： 可以按照任意字段分组， 但分完组后，只能查看分组的那个字段，要想取的组内的其他字段信息，需要借助函数。

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，要获取组内的其他信息，要借助函数。

group by 关键字和 group_concat()函数一起使用。
    select post,group concat(name) from employee group by post;  #按岗位分组，并查看成员名。
    select post,group concat(name) as emp_members from employee group by post;

group ty 与聚合函数一起使用
    select post,count(id) as count from employee group by post;  #按岗位分组，并查看每个组有多少人

强调：

如果我们用unique 的字段做为 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。

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

1.
select post,group_concat(name) from employee group by post;

2.
select post,count(id) from employee group by post;

3.
select sex,count(id) from employee group by sex;

4.
select post,avg(salary) from employee group by post;

5.
select post,max(salary) from employee group by post;

6.
select post,min(salary) from employee group by post;

7.
select sex,avg(salary) from employee group by sex;

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六：使用聚合函数查询

先from找到表

再用where的条件约束去表中取出记录

然后进行分组group by，没有分组则默认一组

然后进行聚合

最后select出结果

示例：
    select count(*) from employee;
    select count(*) from empoloyee where depart_id=1;
    select max(salary) from emploee;
    select min(salary) from employee;
    select avg(salary) from employee;
    select sum(salary) from employee;
    select sum(salary) from employee where depart_id=3;

七：having 过滤

having 与 where 在语法上是一样的。

select * from employee where salary > 10000;
select * from employee having salary > 10000;

不同点：

1.执行优先级：从高到低。
    where > group by > 聚合函数 > having 

2. where 是一个约束条件，是在结果返回之前起作用的。（先找到表，按where的约束条件，取出数据）
    having 是一个过滤条件，是在结果返回以后起作用的。（取出数据后，在group by 分组，如果没有group by 则所有的记录为一组，在执行聚合函数，然后使用having 对聚合的结果进行过滤），在having中可以用聚合函数，where则不能。

3.having 可以放到 group by 之后，而 where 只能放到group by 之前。

4.在查询过程中聚合语句有：
    (sum,min,max,avg,count) 要比having 子句优先执行，
    而where 子句在查询过程中执行优先级高于聚合语句。

验证不同之处：

#验证之前再次强调：执行优先级从高到低：where > group by > 聚合函数 > having 
select count(id) from employee where salary > 10000; #正确，分析：where先执行，后执行聚合count(id),然后select出结果
select count(id) from employee having salary > 10000;#错误，分析：先执行聚合count(id)，后执行having过滤，无法对id进行salary>10000的过滤

#以上两条sql的顺序是
1:找到表employee--->用where过滤---->没有分组则默认一组执行聚合count(id)--->select执行查看组内id数目
2:找到表employee--->没有分组则默认一组执行聚合count(id)---->having 基于上一步聚合的结果（此时只有count(id)字段了）进行salary>10000的过滤，很明显，根本无法获取到salary字段

其他需要注意的问题：

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

1.
select post,group_concat(name),count(id) from empoloyee group by post having count(id) < 2;

2.
select post,avg(salary)  from employee group by post having avg(salary) > 10000;

3.
select post,avg(salary) from employee group by post having avg(salary) > 10000 and avg(salary) < 20000;

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八：查询排序： order by

按单列排序：
    select * from employee oeder by salary;
    select * from employee order by asc;
    select * from employee order by desc;

按多列排序：先按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

1.
select * from employee order by age asc,hire_data desc;

2.
select post,avg(salary) from employee group by post having avg(salary) > 10000 order by avg(salary) asc;

3.
select post,avg(salary) from employee group by post having avg(salary) >10000
order bu avg(salary) desc;

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九： 限制查询的记录数： limit

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：

1. 分页显示，每页5条

#题目1
mysql> select * from employee ORDER BY age asc,hire_date desc;

#题目2
mysql> select post,avg(salary) from employee group by post having avg(salary) > 10000 order by avg(salary) asc;
+-----------+---------------+
| post      | avg(salary)   |
+-----------+---------------+
| operation |  16800.026000 |
| teacher   | 151842.901429 |
+-----------+---------------+

#题目3
mysql> select post,avg(salary) from employee group by post having avg(salary) > 10000 order by avg(salary) desc;
+-----------+---------------+
| post      | avg(salary)   |
+-----------+---------------+
| teacher   | 151842.901429 |
| operation |  16800.026000 |
+-----------+---------------+

回到顶部
十 限制查询的记录数:LIMIT

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：
1. 分页显示，每页5条
 

mysql> select * from  employee limit 0,5;
+----+-----------+------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
| id | name      | sex  | age | hire_date  | post                                    | post_comment | salary     | office | depart_id |
+----+-----------+------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
|  1 | egon      | male |  18 | 2017-03-01 | 老男孩驻沙河办事处外交大使              | NULL         |    7300.33 |    401 |         1 |
|  2 | alex      | male |  78 | 2015-03-02 | teacher                                 |              | 1000000.31 |    401 |         1 |
|  3 | wupeiqi   | male |  81 | 2013-03-05 | teacher                                 | NULL         |    8300.00 |    401 |         1 |
|  4 | yuanhao   | male |  73 | 2014-07-01 | teacher                                 | NULL         |    3500.00 |    401 |         1 |
|  5 | liwenzhou | male |  28 | 2012-11-01 | teacher                                 | NULL         |    2100.00 |    401 |         1 |
+----+-----------+------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
5 rows in set (0.00 sec)

mysql> select * from  employee limit 5,5;
+----+------------+--------+-----+------------+---------+--------------+----------+--------+-----------+
| id | name       | sex    | age | hire_date  | post    | post_comment | salary   | office | depart_id |
+----+------------+--------+-----+------------+---------+--------------+----------+--------+-----------+
|  6 | jingliyang | female |  18 | 2011-02-11 | teacher | NULL         |  9000.00 |    401 |         1 |
|  7 | jinxin     | male   |  18 | 1900-03-01 | teacher | NULL         | 30000.00 |    401 |         1 |
|  8 | 成龙       | male   |  48 | 2010-11-11 | teacher | NULL         | 10000.00 |    401 |         1 |
|  9 | 歪歪       | female |  48 | 2015-03-11 | sale    | NULL         |  3000.13 |    402 |         2 |
| 10 | 丫丫       | female |  38 | 2010-11-01 | sale    | NULL         |  2000.35 |    402 |         2 |
+----+------------+--------+-----+------------+---------+--------------+----------+--------+-----------+
5 rows in set (0.00 sec)

mysql> select * from  employee limit 10,5;
+----+-----------+--------+-----+------------+-----------+--------------+----------+--------+-----------+
| id | name      | sex    | age | hire_date  | post      | post_comment | salary   | office | depart_id |
+----+-----------+--------+-----+------------+-----------+--------------+----------+--------+-----------+
| 11 | 丁丁      | female |  18 | 2011-03-12 | sale      | NULL         |  1000.37 |    402 |         2 |
| 12 | 星星      | female |  18 | 2016-05-13 | sale      | NULL         |  3000.29 |    402 |         2 |
| 13 | 格格      | female |  28 | 2017-01-27 | sale      | NULL         |  4000.33 |    402 |         2 |
| 14 | 张野      | male   |  28 | 2016-03-11 | operation | NULL         | 10000.13 |    403 |         3 |
| 15 | 程咬金    | male   |  18 | 1997-03-12 | operation | NULL         | 20000.00 |    403 |         3 |
+----+-----------+--------+-----+------------+-----------+--------------+----------+--------+-----------+
5 rows in set (0.00 sec)

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十：使用正则表达式查询

select * from employee where name regexp '^ale';

select * from employee where name regexp 'on$';

select * from employee where name regexp 'm{2}';

小结：对字符串匹配的方式
WHERE name = 'egon';
WHERE name LIKE 'yua%';
WHERE name REGEXP 'on$';

小练习：

查看所有员工中名字是jin开头，n或者g结果的员工信息

select * from employee where name regexp '^jin.*[gn]$';