Mysql之查询
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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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