Mysql之查询

一、语法

　　select distinct 查询字段1，查询字段2，...... from 表名

　　　　where 分组之前的过滤条件

　　　　group by分组依据

　　　　having 分组之后的过滤条件

　　　　order by 排序字段

　　　　limit 显示的条数

二、where 过滤

　　表数据如下：

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)
;
#查询记录

mysql> select * from employee;
+----+------------+--------+-----+------------+----------------------------+--------------+------------+--------+-----------+
| 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 | NULL | 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 |
| 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 |
| 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 |
| 16 | 程咬银 | female | 18 | 2013-03-11 | operation | NULL | 19000.00 | 403 | 3 |
| 17 | 程咬铜 | male | 18 | 2015-04-11 | operation | NULL | 18000.00 | 403 | 3 |
| 18 | 程咬铁 | female | 18 | 2014-05-12 | operation | NULL | 17000.00 | 403 | 3 |
+----+------------+--------+-----+------------+----------------------------+--------------+------------+--------+-----------+

要求：查询员工姓名中包含i字母的员工与其薪资

alter table employee rename emp;

select name,salary from db1.emp where name like '%i%'

#得到的结果如下：
+------------+----------+
| name       | salary   |
+------------+----------+
| wupeiqi    |  8300.00 |
| liwenzhou  |  2100.00 |
| jingliyang |  9000.00 |
| jinxin     | 30000.00 |
+------------+----------+

要求：查询员工姓名是由四个字符组成的员工姓名和薪资

select name,salary from db1.emp where name like '____';

or

select name,salary from db1.emp where char_length(name) = 4;

#得到的结果如下
mysql> select name,salary from emp where name like '____';
+------+------------+
| name | salary     |
+------+------------+
| egon |    7300.33 |
| alex | 1000000.31 |
+------+------------+

要求：查询岗位描述为空(非空)的员工名与岗位名

select name,post from emp where post_comment is NULL;

select name.post from emp where post_comment is not NULL;

#得到的结果如下：
+------------+----------------------------+
| name       | post                       |
+------------+----------------------------+
| egon       | 老男孩驻沙河办事处外交大使 |
| alex       | teacher                    |
| wupeiqi    | teacher                    |
| yuanhao    | teacher                    |
| liwenzhou  | teacher                    |
| jingliyang | teacher                    |
| jinxin     | teacher                    |
| 成龙       | teacher                    |
| 歪歪       | sale                       |
| 丫丫       | sale                       |
| 丁丁       | sale                       |
| 星星       | sale                       |
| 格格       | sale                       |
| 张野       | operation                  |
| 程咬金     | operation                  |
| 程咬银     | operation                  |
| 程咬铜     | operation                  |
| 程咬铁     | operation                  |
+------------+----------------------------+

三、group by 分组

#设置sql_mode为only_full_group_by,意味着以后但凡分组，只能取到分组的依据
   
  mysql> set global sql_mode="strict_trans_tables,only_full_group_by";

#每个部分的最高工资
select post,max(salary) from emp group by post;
+----------------------------+-------------+
| post                       | max(salary) |
+----------------------------+-------------+
| operation                  |    20000.00 |
| sale                       |     4000.33 |
| teacher                    |  1000000.31 |
| 老男孩驻沙河办事处外交大使 |     7300.33 |
+----------------------------+-------------+

#每个部门最低工资
select post,min(salary) from emp group by post;
+----------------------------+-------------+
| post                       | min(salary) |
+----------------------------+-------------+
| operation                  |    10000.13 |
| sale                       |     1000.37 |
| teacher                    |     2100.00 |
| 老男孩驻沙河办事处外交大使 |     7300.33 |
+----------------------------+-------------+

#每个部门的平均工资
select post,avg(salary) from emp group by post;
+----------------------------+---------------+
| post                       | avg(salary)   |
+----------------------------+---------------+
| operation                  |  16800.026000 |
| sale                       |   2600.294000 |
| teacher                    | 151842.901429 |
| 老男孩驻沙河办事处外交大使 |   7300.330000 |
+----------------------------+---------------+

#每个部门工资的总和
select post,sum(salary) from emp group by post;
+----------------------------+-------------+
| post                       | sum(salary) |
+----------------------------+-------------+
| operation                  |    84000.13 |
| sale                       |    13001.47 |
| teacher                    |  1062900.31 |
| 老男孩驻沙河办事处外交大使 |     7300.33 |
+----------------------------+-------------+

每个部门的人数
select post,count(id) from emp group by post;
+----------------------------+-----------+
| post                       | count(id) |
+----------------------------+-----------+
| operation                  |         5 |
| sale                       |         5 |
| teacher                    |         7 |
| 老男孩驻沙河办事处外交大使 |         1 |
+----------------------------+-----------+

补充 group_concat

select post,group_concat(name) from emp group by post;
+----------------------------+-------------------------------------------------------+
| post                       | group_concat(name)                                    |
+----------------------------+-------------------------------------------------------+
| operation                  | 程咬铁,程咬铜,程咬银,程咬金,张野                      |
| sale                       | 格格,星星,丁丁,丫丫,歪歪                              |
| teacher                    | 成龙,jinxin,jingliyang,liwenzhou,yuanhao,wupeiqi,alex |
| 老男孩驻沙河办事处外交大使 | egon                                                  |
+----------------------------+-------------------------------------------------------+



select post,group_concat(name ':' salary) from emp group by post;
+----------------------------+--------------------------------------------------------------------------------------------------------------------+
| post                       | group_concat(name,':',salary)                                                                                      |
+----------------------------+--------------------------------------------------------------------------------------------------------------------+
| operation                  | 程咬铁:17000.00,程咬铜:18000.00,程咬银:19000.00,程咬金:20000.00,张野:10000.13                                      |
| sale                       | 格格:4000.33,星星:3000.29,丁丁:1000.37,丫丫:2000.35,歪歪:3000.13                                                   |
| teacher                    | 成龙:10000.00,jinxin:30000.00,jingliyang:9000.00,liwenzhou:2100.00,yuanhao:3500.00,wupeiqi:8300.00,alex:1000000.31 |
| 老男孩驻沙河办事处外交大使 | egon:7300.33                                                                                                       |
+----------------------------+--------------------------------------------------------------------------------------------------------------------+

补充concat，单独使用时：

mysql> select concat(name,':',salary) from emp where age=18;
+-------------------------+
| concat(name,':',salary) |
+-------------------------+
| egon:7300.33            |
| jingliyang:9000.00      |
| jinxin:30000.00         |
| 丁丁:1000.37            |
| 星星:3000.29            |
| 程咬金:20000.00         |
| 程咬银:19000.00         |
| 程咬铜:18000.00         |
| 程咬铁:17000.00         |
+-------------------------+

mysql> select concat(name,':',salary) as '薪水' from emp where age=18;
+--------------------+
| 薪水               |
+--------------------+
| egon:7300.33       |
| jingliyang:9000.00 |
| jinxin:30000.00    |
| 丁丁:1000.37       |
| 星星:3000.29       |
| 程咬金:20000.00    |
| 程咬银:19000.00    |
| 程咬铜:18000.00    |
| 程咬铁:17000.00    |
+--------------------+

#补充：连表操作获取一个部门最高薪资的人的信息

#获取post表
select post,max(salary) from emp group by post;

#连接两表
 select t1.name,t1.salary from emp as t1 inner join (select post,max(salary) as ms from emp group by post) as t2 on t1.salary = t2.ms;

+--------+------------+
| name   | salary     |
+--------+------------+
| egon   |    7300.33 |
| alex   | 1000000.31 |
| 格格   |    4000.33 |
| 程咬金 |   20000.00 |
+--------+------------+

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