一、单表查询的语法
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）
1、from 库.表——找到表 2、where 条件——按照where指定的约束条件，去表中取出一条条记录 3、group by 分组条件——对取出的一条条记录分组，如果没有group by，整体作为一组 4、having 过滤——将分组的结果进行过滤 5、select——从虚拟表选择出需要的内容 6、distinct——去重，如果在查询中指定了DISTINCT子句，则会创建一张内存临时表（如果内存放不下，就需要存放在硬盘了）。这张临时表的表结构和上一步产生的虚拟表VT7是一样的，不同的是对进行DISTINCT操作的列增加了一个唯一索引，以此来除重复数据。 7、order by 排序字段——对虚拟表中的内容按照指定的列进行排序，然后返回一个新的虚拟表 8、limit n;——限制结果的显示条数，LIMIT子句从上一步得到的VT8虚拟表中选出从指定位置开始的指定行数据。对于没有应用ORDER BY的LIMIT子句，得到的结果同样是无序的，所以，很多时候，我们都会看到LIMIT子句会和ORDER BY子句一起使用
详细见：http://www.cnblogs.com/linhaifeng/articles/7372774.html
三、简单查询
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,'','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,'','teacher',1000000.31,401,1),
('wupeiqi','male',81,'','teacher',8300,401,1),
('yuanhao','male',73,'','teacher',3500,401,1),
('liwenzhou','male',28,'','teacher',2100,401,1),
('jingliyang','female',18,'','teacher',9000,401,1),
('jinxin','male',18,'','teacher',30000,401,1),
('成龙','male',48,'','teacher',10000,401,1), ('歪歪','female',48,'','sale',3000.13,402,2),#以下是销售部门
('丫丫','female',38,'','sale',2000.35,402,2),
('丁丁','female',18,'','sale',1000.37,402,2),
('星星','female',18,'','sale',3000.29,402,2),
('格格','female',28,'','sale',4000.33,402,2), ('张野','male',28,'','operation',10000.13,403,3), #以下是运营部门
('程咬金','male',18,'','operation',20000,403,3),
('程咬银','female',18,'','operation',19000,403,3),
('程咬铜','male',18,'','operation',18000,403,3),
('程咬铁','female',18,'','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,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; 结合CASE语句：
SELECT
(
CASE
WHEN NAME = 'egon' THEN
NAME
WHEN NAME = 'alex' THEN
CONCAT(name,'_BIGSB')
ELSE
concat(NAME, 'SB')
END
) as new_name
FROM
emp;
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 |
+----+------------+--------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
18 rows in set (0.00 sec) mysql> select id,name,salary from employee;
+----+------------+------------+
| id | name | salary |
+----+------------+------------+
| 1 | egon | 7300.33 |
| 2 | alex | 1000000.31 |
| 3 | wupeiqi | 8300.00 |
| 4 | yuanhao | 3500.00 |
| 5 | liwenzhou | 2100.00 |
| 6 | jingliyang | 9000.00 |
| 7 | jinxin | 30000.00 |
| 8 | 成龙 | 10000.00 |
| 9 | 歪歪 | 3000.13 |
| 10 | 丫丫 | 2000.35 |
| 11 | 丁丁 | 1000.37 |
| 12 | 星星 | 3000.29 |
| 13 | 格格 | 4000.33 |
| 14 | 张野 | 10000.13 |
| 15 | 程咬金 | 20000.00 |
| 16 | 程咬银 | 19000.00 |
| 17 | 程咬铜 | 18000.00 |
| 18 | 程咬铁 | 17000.00 |
+----+------------+------------+
18 rows in set (0.00 sec)
简单查询
在需要去重查询时，可以利用distinct去除重复信息。
# distinct去除重复的职位信息
mysql> select distinct post from employee;
+-----------------------------------------+
| post |
+-----------------------------------------+
| 老男孩驻沙河办事处外交大使 |
| teacher |
| sale |
| operation |
+-----------------------------------------+
4 rows in set (0.00 sec)
避免重复DISTINCT
利用四则运算查询（加减乘除）得到需要的查询结果。针对四则运算的字段还可以取别名，以优化显示结果。
# 查看一个人的年薪
mysql> select name, salary*12 from employee;
+------------+-------------+
| name | salary*12 |
+------------+-------------+
| egon | 87603.96 |
| alex | 12000003.72 |
| wupeiqi | 99600.00 |
| yuanhao | 42000.00 |
| liwenzhou | 25200.00 |
| jingliyang | 108000.00 |
| jinxin | 360000.00 |
| 成龙 | 120000.00 |
| 歪歪 | 36001.56 |
| 丫丫 | 24004.20 |
| 丁丁 | 12004.44 |
| 星星 | 36003.48 |
| 格格 | 48003.96 |
| 张野 | 120001.56 |
| 程咬金 | 240000.00 |
| 程咬银 | 228000.00 |
| 程咬铜 | 216000.00 |
| 程咬铁 | 204000.00 |
+------------+-------------+
18 rows in set (0.00 sec) # 给年薪起一个别名
mysql> select name, salary*12 as Annual_salary from employee;
+------------+---------------+
| name | Annual_salary |
+------------+---------------+
| egon | 87603.96 |
| alex | 12000003.72 |
| wupeiqi | 99600.00 |
| yuanhao | 42000.00 |
| liwenzhou | 25200.00 |
| jingliyang | 108000.00 |
| jinxin | 360000.00 |
| 成龙 | 120000.00 |
| 歪歪 | 36001.56 |
| 丫丫 | 24004.20 |
| 丁丁 | 12004.44 |
| 星星 | 36003.48 |
| 格格 | 48003.96 |
| 张野 | 120001.56 |
| 程咬金 | 240000.00 |
| 程咬银 | 228000.00 |
| 程咬铜 | 216000.00 |
| 程咬铁 | 204000.00 |
+------------+---------------+
18 rows in set (0.00 sec) # 起别名不加as的方法
mysql> select name, salary*12 Annual_salary from employee;
+------------+---------------+
| name | Annual_salary |
+------------+---------------+
| egon | 87603.96 |
| alex | 12000003.72 |
| wupeiqi | 99600.00 |
| yuanhao | 42000.00 |
| liwenzhou | 25200.00 |
| jingliyang | 108000.00 |
| jinxin | 360000.00 |
| 成龙 | 120000.00 |
| 歪歪 | 36001.56 |
| 丫丫 | 24004.20 |
| 丁丁 | 12004.44 |
| 星星 | 36003.48 |
| 格格 | 48003.96 |
| 张野 | 120001.56 |
| 程咬金 | 240000.00 |
| 程咬银 | 228000.00 |
| 程咬铜 | 216000.00 |
| 程咬铁 | 204000.00 |
+------------+---------------+
18 rows in set (0.00 sec)
四则运算及取别名方法
利用concat和逗号*定义显示格式
# concat()函数用于连接字符串
mysql> select concat('姓名:',name) from employee;
+------------------------+
| concat('姓名:',name) |
+------------------------+
| 姓名:egon |
| 姓名:alex |
| 姓名:wupeiqi |
| 姓名:yuanhao |
| 姓名:liwenzhou |
| 姓名:jingliyang |
| 姓名:jinxin |
| 姓名:成龙 |
| 姓名:歪歪 |
| 姓名:丫丫 |
| 姓名:丁丁 |
| 姓名:星星 |
| 姓名:格格 |
| 姓名:张野 |
| 姓名:程咬金 |
| 姓名:程咬银 |
| 姓名:程咬铜 |
| 姓名:程咬铁 |
+------------------------+
18 rows in set (0.00 sec) mysql> select concat('姓名:',name,'性别:',sex,'年薪:',salary*12) as emp_info_salary from employee; # as设置查询结果标题
+------------------------------------------------+
| emp_info_salary |
+------------------------------------------------+
| 姓名:egon性别:male年薪:87603.96 |
| 姓名:alex性别:male年薪:12000003.72 |
| 姓名:wupeiqi性别:male年薪:99600.00 |
| 姓名:yuanhao性别:male年薪:42000.00 |
| 姓名:liwenzhou性别:male年薪:25200.00 |
| 姓名:jingliyang性别:female年薪:108000.00 |
| 姓名:jinxin性别:male年薪:360000.00 |
| 姓名:成龙性别:male年薪:120000.00 |
| 姓名:歪歪性别:female年薪:36001.56 |
| 姓名:丫丫性别:female年薪:24004.20 |
| 姓名:丁丁性别:female年薪:12004.44 |
| 姓名:星星性别:female年薪:36003.48 |
| 姓名:格格性别:female年薪:48003.96 |
| 姓名:张野性别:male年薪:120001.56 |
| 姓名:程咬金性别:male年薪:240000.00 |
| 姓名:程咬银性别:female年薪:228000.00 |
| 姓名:程咬铜性别:male年薪:216000.00 |
| 姓名:程咬铁性别:female年薪:204000.00 |
+------------------------------------------------+
18 rows in set (0.00 sec) # 想把薪资单独分出来，用concat和逗号拼接出想要的格式
mysql> select concat('姓名:',name,'性别:',sex) as info, concat('年薪:', salary*12) as annual_salary from employee;
+--------------------------------+--------------------+
| info | annual_salary |
+--------------------------------+--------------------+
| 姓名:egon性别:male | 年薪:87603.96 |
| 姓名:alex性别:male | 年薪:12000003.72 |
| 姓名:wupeiqi性别:male | 年薪:99600.00 |
| 姓名:yuanhao性别:male | 年薪:42000.00 |
| 姓名:liwenzhou性别:male | 年薪:25200.00 |
| 姓名:jingliyang性别:female | 年薪:108000.00 |
| 姓名:jinxin性别:male | 年薪:360000.00 |
| 姓名:成龙性别:male | 年薪:120000.00 |
| 姓名:歪歪性别:female | 年薪:36001.56 |
| 姓名:丫丫性别:female | 年薪:24004.20 |
| 姓名:丁丁性别:female | 年薪:12004.44 |
| 姓名:星星性别:female | 年薪:36003.48 |
| 姓名:格格性别:female | 年薪:48003.96 |
| 姓名:张野性别:male | 年薪:120001.56 |
| 姓名:程咬金性别:male | 年薪:240000.00 |
| 姓名:程咬银性别:female | 年薪:228000.00 |
| 姓名:程咬铜性别:male | 年薪:216000.00 |
| 姓名:程咬铁性别:female | 年薪:204000.00 |
+--------------------------------+--------------------+
18 rows in set (0.00 sec)
concat()函数连接字符串
# concat_ws() 第一个参数为分隔符，处理多条记录+分隔符更方便
mysql> select concat_ws(':', name, sex, salary) as emp_info from employee;
+---------------------------+
| emp_info |
+---------------------------+
| egon:male:7300.33 |
| alex:male:1000000.31 |
| wupeiqi:male:8300.00 |
| yuanhao:male:3500.00 |
| liwenzhou:male:2100.00 |
| jingliyang:female:9000.00 |
| jinxin:male:30000.00 |
| 成龙:male:10000.00 |
| 歪歪:female:3000.13 |
| 丫丫:female:2000.35 |
| 丁丁:female:1000.37 |
| 星星:female:3000.29 |
| 格格:female:4000.33 |
| 张野:male:10000.13 |
| 程咬金:male:20000.00 |
| 程咬银:female:19000.00 |
| 程咬铜:male:18000.00 |
| 程咬铁:female:17000.00 |
+---------------------------+
18 rows in set (0.00 sec)
concat_ws()优化处理记录和分隔符
结合case语句，自定义复杂的显示格式。
# 结合CASE语句
mysql> SELECT
-> (
-> CASE
-> WHEN NAME = 'egon' THEN
-> NAME
-> WHEN NAME = 'alex' THEN
-> CONCAT(name,'_BIGSB')
-> ELSE
-> concat(NAME, 'SB')
-> END
-> ) as new_name
-> FROM
-> employee;
+--------------+
| new_name |
+--------------+
| egon |
| alex_BIGSB |
| wupeiqiSB |
| yuanhaoSB |
| liwenzhouSB |
| jingliyangSB |
| jinxinSB |
| 成龙SB |
| 歪歪SB |
| 丫丫SB |
| 丁丁SB |
| 星星SB |
| 格格SB |
| 张野SB |
| 程咬金SB |
| 程咬银SB |
| 程咬铜SB |
| 程咬铁SB |
+--------------+
18 rows in set (0.00 sec)
CASE语句自定义查询结果
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、查出所有岗位(去掉重复)
3、查出所有员工名字，以及他们的年薪，年薪字段名为annual_year
mysql> select concat("<名字:",name,">") as NAME, concat("<薪资:",salary,">") as SALARY from employee;
+---------------------+---------------------+
| NAME | SALARY |
+---------------------+---------------------+
| <名字:egon> | <薪资:7300.33> |
| <名字:alex> | <薪资:1000000.31> |
| <名字:wupeiqi> | <薪资:8300.00> |
| <名字:yuanhao> | <薪资:3500.00> |
| <名字:liwenzhou> | <薪资:2100.00> |
| <名字:jingliyang> | <薪资:9000.00> |
| <名字:jinxin> | <薪资:30000.00> |
| <名字:成龙> | <薪资:10000.00> |
| <名字:歪歪> | <薪资:3000.13> |
| <名字:丫丫> | <薪资:2000.35> |
| <名字:丁丁> | <薪资:1000.37> |
| <名字:星星> | <薪资:3000.29> |
| <名字:格格> | <薪资:4000.33> |
| <名字:张野> | <薪资:10000.13> |
| <名字:程咬金> | <薪资:20000.00> |
| <名字:程咬银> | <薪资:19000.00> |
| <名字:程咬铜> | <薪资:18000.00> |
| <名字:程咬铁> | <薪资:17000.00> |
+---------------------+---------------------+
18 rows in set (0.00 sec)
mysql> select distinct post from employee;
+-----------------------------------------+
| post |
+-----------------------------------------+
| 老男孩驻沙河办事处外交大使 |
| teacher |
| sale |
| operation |
+-----------------------------------------+
4 rows in set (0.00 sec)
mysql> select name, salary*12 as annual_year from employee;
+------------+-------------+
| name | annual_year |
+------------+-------------+
| egon | 87603.96 |
| alex | 12000003.72 |
| wupeiqi | 99600.00 |
| yuanhao | 42000.00 |
| liwenzhou | 25200.00 |
| jingliyang | 108000.00 |
| jinxin | 360000.00 |
| 成龙 | 120000.00 |
| 歪歪 | 36001.56 |
| 丫丫 | 24004.20 |
| 丁丁 | 12004.44 |
| 星星 | 36003.48 |
| 格格 | 48003.96 |
| 张野 | 120001.56 |
| 程咬金 | 240000.00 |
| 程咬银 | 228000.00 |
| 程咬铜 | 216000.00 |
| 程咬铁 | 204000.00 |
+------------+-------------+
18 rows in set (0.00 sec)
练习题答案
四、WHERE约束
where字句可以使用：
1、比较运算符：> < >= <= ; <> != (这两个不等于符号，一般采用!=)
2、between 80 and 100 指的就是大于等于80，小于等于100
3、in(80,90,100) 满足在这个范围内，值是80或90或100
4、like 'egon%' 这种是模糊匹配
pattern可以是%或_，
%表示任意多字符；_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(与) or（或） not(非)
#1:单条件查询
SELECT name FROM employee
WHERE post='sale'; #2:多条件查询 (AND串联条件)
SELECT name,salary FROM employee
WHERE post='teacher' AND salary>10000; #3:关键字BETWEEN AND
SELECT name,salary FROM employee
WHERE salary BETWEEN 10000 AND 20000; SELECT 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 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，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 name,salary FROM employee
WHERE salary=3000 OR salary=3500 OR salary=4000 OR salary=9000 ; SELECT name,salary FROM employee
WHERE salary IN (3000,3500,4000,9000) ; SELECT 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 name LIKE 'eg%'; 通配符’_’
SELECT * FROM employee
WHERE name LIKE 'al__';
# 1、单条件查询
mysql> select id,name,age from employee where id > 7;
+----+-----------+-----+
| id | name | age |
+----+-----------+-----+
| 8 | 成龙 | 48 |
| 9 | 歪歪 | 48 |
| 10 | 丫丫 | 38 |
| 11 | 丁丁 | 18 |
| 12 | 星星 | 18 |
| 13 | 格格 | 28 |
| 14 | 张野 | 28 |
| 15 | 程咬金 | 18 |
| 16 | 程咬银 | 18 |
| 17 | 程咬铜 | 18 |
| 18 | 程咬铁 | 18 |
+----+-----------+-----+
11 rows in set (0.00 sec) mysql> select name from employee where post='sale';
+--------+
| name |
+--------+
| 歪歪 |
| 丫丫 |
| 丁丁 |
| 星星 |
| 格格 |
+--------+
5 rows in set (0.00 sec) # 2、多条件查询(AND串联)
mysql> select name,salary from employee
-> where post='teacher' and salary>10000;
+--------+------------+
| name | salary |
+--------+------------+
| alex | 1000000.31 |
| jinxin | 30000.00 |
+--------+------------+
2 rows in set (0.00 sec) mysql> select * from employee where post ='teacher' and salary>8000;
+----+------------+--------+-----+------------+---------+--------------+------------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+------------+--------+-----+------------+---------+--------------+------------+--------+-----------+
| 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 |
| 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 |
+----+------------+--------+-----+------------+---------+--------------+------------+--------+-----------+
5 rows in set (0.00 sec) # 3、关键字BETWEEN x AND y ————大于等于x，小于等于y
mysql> select name,salary from employee
-> where salary between 10000 and 20000;
+-----------+----------+
| name | salary |
+-----------+----------+
| 成龙 | 10000.00 |
| 张野 | 10000.13 |
| 程咬金 | 20000.00 |
| 程咬银 | 19000.00 |
| 程咬铜 | 18000.00 |
| 程咬铁 | 17000.00 |
+-----------+----------+
6 rows in set (0.01 sec) mysql> select name,salary from employee
-> where salary NOT BETWEEN 10000 AND 20000; # 10000以下，20000以上
+------------+------------+
| name | salary |
+------------+------------+
| egon | 7300.33 |
| alex | 1000000.31 |
| wupeiqi | 8300.00 |
| yuanhao | 3500.00 |
| liwenzhou | 2100.00 |
| jingliyang | 9000.00 |
| jinxin | 30000.00 |
| 歪歪 | 3000.13 |
| 丫丫 | 2000.35 |
| 丁丁 | 1000.37 |
| 星星 | 3000.29 |
| 格格 | 4000.33 |
+------------+------------+
12 rows in set (0.00 sec) #4:关键字IN集合查询
mysql> select * from employee where salary=3000 or salary=3500 or salary=4000 or salary=9000;
+----+------------+--------+-----+------------+---------+--------------+---------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+------------+--------+-----+------------+---------+--------------+---------+--------+-----------+
| 4 | yuanhao | male | 73 | 2014-07-01 | teacher | NULL | 3500.00 | 401 | 1 |
| 6 | jingliyang | female | 18 | 2011-02-11 | teacher | NULL | 9000.00 | 401 | 1 |
+----+------------+--------+-----+------------+---------+--------------+---------+--------+-----------+
2 rows in set (0.00 sec) mysql> select * from employee
-> where salary in (3000,3500,4000,9000);
+----+------------+--------+-----+------------+---------+--------------+---------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+------------+--------+-----+------------+---------+--------------+---------+--------+-----------+
| 4 | yuanhao | male | 73 | 2014-07-01 | teacher | NULL | 3500.00 | 401 | 1 |
| 6 | jingliyang | female | 18 | 2011-02-11 | teacher | NULL | 9000.00 | 401 | 1 |
+----+------------+--------+-----+------------+---------+--------------+---------+--------+-----------+
2 rows in set (0.01 sec) mysql> select * from employee where salary not in (3000,3500,4000,9000);
+----+-----------+--------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
| 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 |
| 5 | liwenzhou | male | 28 | 2012-11-01 | teacher | NULL | 2100.00 | 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 |
+----+-----------+--------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
16 rows in set (0.00 sec) #5:关键字IS NULL(判断某个字段是否为NULL不能用等号，需要用IS)
# 注意NULL和''空字符串是不同的
mysql> select * from employee
-> where post_comment is null;
+----+------------+--------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
| 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 |
+----+------------+--------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
18 rows in set (0.00 sec) # is not NULL取反
mysql> select * from employee where post_comment is not null;
Empty set (0.00 sec) mysql> select * from employee where post_comment=''; # 注意‘’空字符串不是null
Empty set (0.00 sec) #6：关键字LIKE模糊匹配
mysql> select * from employee
-> where name like 'eg%'; # 任意个数任意字符
+----+------+------+-----+------------+-----------------------------------------+--------------+---------+--------+-----------+
| 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 |
+----+------+------+-----+------------+-----------------------------------------+--------------+---------+--------+-----------+
1 row in set (0.01 sec) mysql> select * from employee
-> where name like 'al__'; # 一个'_'对应一个任意字符
+----+------+------+-----+------------+---------+--------------+------------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+------+------+-----+------------+---------+--------------+------------+--------+-----------+
| 2 | alex | male | 78 | 2015-03-02 | teacher | NULL | 1000000.31 | 401 | 1 |
+----+------+------+-----+------------+---------+--------------+------------+--------+-----------+
1 row in set (0.00 sec)
where约束操作示例
五、分组查询：GROUP BY
1、什么是分组？为什么要分组？
1、分组发生在where之后，即分组是基于where之后得到的记录而进行的
2、分组指的是：将所有记录按照某个相同字段进行归类，比如针对员工信息表的职位分组，或者按照性别进行分组等。
3、为什么要分组：分门别类地进行处理。
每个部门员工、男人与女人数等，“每”这个字后面的字段，就是我们的分组依据。
4、大前提：可以按照任意字段分组，但是分组完毕后，比如group by post，只能查看post字段，如果想查看组内信息，需要借助于聚合函数。
2、ONLY_FULL_GROUP_BY
#查看MySQL 5.7默认的sql_mode如下：
mysql> select @@global.sql_mode;
ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION #！！！注意
ONLY_FULL_GROUP_BY的语义就是确定select target list中的所有列的值都是明确语义，简单的说来，在ONLY_FULL_GROUP_BY模式下，
target list中的值要么是来自于聚集函数的结果，要么是来自于group by list中的表达式的值。 #设置sql_mole如下操作(我们可以去掉ONLY_FULL_GROUP_BY模式)：
mysql> set global sql_mode='STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION';
在没有设置ONLY_FULL_GROUP_BY时，在分组的情况下查看到其他字段的信息，也可以有结果，默认都是组内的第一条记录。但是这个的意义不大。
mysql> select @@global.sql_mode;
+-------------------+
| @@global.sql_mode |
+-------------------+
| |
+-------------------+
1 row in set (0.00 sec) mysql> select * from emp group by post;
+----+------+--------+-----+------------+----------------------------+--------------+------------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+------+--------+-----+------------+----------------------------+--------------+------------+--------+-----------+
| 14 | 张野 | male | 28 | 2016-03-11 | operation | NULL | 10000.13 | 403 | 3 |
| 9 | 歪歪 | female | 48 | 2015-03-11 | sale | NULL | 3000.13 | 402 | 2 |
| 2 | alex | male | 78 | 2015-03-02 | teacher | NULL | 1000000.31 | 401 | 1 |
| 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 |
+----+------+--------+-----+------------+----------------------------+--------------+------------+--------+-----------+
4 rows in set (0.00 sec) #由于没有设置ONLY_FULL_GROUP_BY,于是也可以有结果，默认都是组内的第一条记录，但其实这是没有意义的 mysql> set global sql_mode='ONLY_FULL_GROUP_BY';
Query OK, 0 rows affected (0.00 sec) mysql> quit #设置成功后，一定要退出，然后重新登录方可生效
Bye mysql> use db1;
Database changed
mysql> select * from emp group by post; #报错
ERROR 1055 (42000): 'db1.emp.id' isn't in GROUP BY
mysql> select post,count(id) from emp group by post; #只能查看分组依据和使用聚合函数
+----------------------------+-----------+
| post | count(id) |
+----------------------------+-----------+
| operation | 5 |
| sale | 5 |
| teacher | 7 |
| 老男孩驻沙河办事处外交大使 | 1 |
+----------------------------+-----------+
4 rows in set (0.00 sec)
3、GROUP BY
（1）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。
mysql> select post from employee GROUP BY post;
+-----------------------------------------+
| post |
+-----------------------------------------+
| operation |
| sale |
| teacher |
| 老男孩驻沙河办事处外交大使 |
+-----------------------------------------+
4 rows in set (0.01 sec) mysql> select * from employee GROUP BY post;
ERROR 1055 (42000): Expression #1 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'db2.employee.id' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by
（2）GROUP BY关键字和GROUP_CONCAT()函数一起使用
GROUP_CONCAT()函数将对组里的对应记录进行拼接。
#按照岗位分组，并查看组内成员名
mysql> SELECT post,GROUP_CONCAT(name) FROM employee GROUP BY post;
+-----------------------------------------+---------------------------------------------------------+
| post | GROUP_CONCAT(name) |
+-----------------------------------------+---------------------------------------------------------+
| operation | 张野,程咬金,程咬银,程咬铜,程咬铁 |
| sale | 歪歪,丫丫,丁丁,星星,格格 |
| teacher | alex,wupeiqi,yuanhao,liwenzhou,jingliyang,jinxin,成龙 |
| 老男孩驻沙河办事处外交大使 | egon |
+-----------------------------------------+---------------------------------------------------------+
4 rows in set (0.00 sec) mysql> SELECT post,GROUP_CONCAT(name) as emp_members FROM employee GROUP BY post;
+-----------------------------------------+---------------------------------------------------------+
| post | emp_members |
+-----------------------------------------+---------------------------------------------------------+
| operation | 张野,程咬金,程咬银,程咬铜,程咬铁 |
| sale | 歪歪,丫丫,丁丁,星星,格格 |
| teacher | alex,wupeiqi,yuanhao,liwenzhou,jingliyang,jinxin,成龙 |
| 老男孩驻沙河办事处外交大使 | egon |
+-----------------------------------------+---------------------------------------------------------+
4 rows in set (0.00 sec)
（3）GROUP BY与聚合函数一起使用
mysql> 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
+-----------------------------------------+-------+
| post | count |
+-----------------------------------------+-------+
| operation | 5 |
| sale | 5 |
| teacher | 7 |
| 老男孩驻沙河办事处外交大使 | 1 |
+-----------------------------------------+-------+
4 rows in set (0.00 sec)
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。
分组之后，只能取分组的字段，以及每个组聚合函数的结果。
4、聚合函数
注意：聚合函数聚合的是组的内容，若没有分组，则默认分为一组，因此没有分组也可以使用聚合函数。常用聚合函数如下：
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;
# 利用聚合函数查看分组情况
# 统计每个部门员工人数
mysql> select count(id) from employee group by post;
+-----------+
| count(id) |
+-----------+
| 5 |
| 5 |
| 7 |
| 1 |
+-----------+
4 rows in set (0.00 sec) # 统计公司总人数
mysql> select count(*) from employee;
+----------+
| count(*) |
+----------+
| 18 |
+----------+
1 row in set (0.00 sec) # 每个职位有多少个员工？count()
mysql> select post, count(id) from employee 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 |
+-----------------------------------------+-----------+
4 rows in set (0.00 sec) # 为员工统计取别名 count()
mysql> select post,count(id) as emp_count from employee group by post;
+-----------------------------------------+-----------+
| post | emp_count |
+-----------------------------------------+-----------+
| operation | 5 |
| sale | 5 |
| teacher | 7 |
| 老男孩驻沙河办事处外交大使 | 1 |
+-----------------------------------------+-----------+
4 rows in set (0.00 sec) # 取每个部门的最大工资sum()
mysql> select post,max(salary) as max_salary from employee 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 |
+-----------------------------------------+------------+
4 rows in set (0.00 sec) # 取每个部门最小工资，min()
mysql> select post,min(salary) as min_salary from employee 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 |
+-----------------------------------------+------------+
4 rows in set (0.00 sec) # 取每个部门的平均工资，avg()
mysql> select post,avg(salary) as avg_salary from employee 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 |
+-----------------------------------------+---------------+
4 rows in set (0.00 sec) # 取每个部门员工工资总和，sum()
mysql> select post,sum(salary) as sum_salary from employee 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 |
+-----------------------------------------+------------+
4 rows in set (0.00 sec) # 取id为3的部门员工年龄总和
mysql> select post,sum(age) from employee where depart_id =3 group by post;
+-----------+----------+
| post | sum(age) |
+-----------+----------+
| operation | 100 |
+-----------+----------+
1 row in set (0.00 sec) mysql> select post,sum(age) from employee where depart_id =3 group by post;
聚合函数操作实例
5、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
练习题
mysql> select post,GROUP_CONCAT(name) as dev_members from employee group by post;
+-----------------------------------------+---------------------------------------------------------+
| post | dev_members |
+-----------------------------------------+---------------------------------------------------------+
| operation | 张野,程咬金,程咬银,程咬铜,程咬铁 |
| sale | 歪歪,丫丫,丁丁,星星,格格 |
| teacher | alex,wupeiqi,yuanhao,liwenzhou,jingliyang,jinxin,成龙 |
| 老男孩驻沙河办事处外交大使 | egon |
+-----------------------------------------+---------------------------------------------------------+
4 rows in set (0.00 sec) mysql> select post,count(id) from employee 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 |
+-----------------------------------------+-----------+
4 rows in set (0.00 sec) mysql> select sex,count(id) from employee group by sex;
+--------+-----------+
| sex | count(id) |
+--------+-----------+
| male | 10 |
| female | 8 |
+--------+-----------+
2 rows in set (0.00 sec) mysql> select post,avg(salary) as avg_salary from employee 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 |
+-----------------------------------------+---------------+
4 rows in set (0.00 sec) mysql> select post,max(salary) as max_salary from employee 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 |
+-----------------------------------------+------------+
4 rows in set (0.00 sec) mysql> select post,min(salary) as min_salary from employee 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 |
+-----------------------------------------+------------+
4 rows in set (0.00 sec) mysql> select sex,avg(salary) as avg_sex_salary from employee group by sex;
+--------+----------------+
| sex | avg_sex_salary |
+--------+----------------+
| male | 110920.077000 |
| female | 7250.183750 |
+--------+----------------+
2 rows in set (0.00 sec)
练习题答案
六、HAVING过滤
HAVING与WHERE不一样的地方？
执行优先级从高到低：where > group by > having
1、where发生在分组group by之前，因此where中可以有任意字段，但是绝对不能使用聚合函数。
2、having发生分组group by之后，因此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。
mysql> select @@sql_mode;
+-------------------------------------------------------------------------------------------------------------------------------------------+
| @@sql_mode |
+-------------------------------------------------------------------------------------------------------------------------------------------+
| ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION |
+-------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec) mysql> select * from employee where salary > 10000;
+----+-----------+--------+-----+------------+-----------+--------------+------------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+-----------+--------+-----+------------+-----------+--------------+------------+--------+-----------+
| 2 | alex | male | 78 | 2015-03-02 | teacher | NULL | 1000000.31 | 401 | 1 |
| 7 | jinxin | male | 18 | 1900-03-01 | teacher | NULL | 30000.00 | 401 | 1 |
| 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 |
+----+-----------+--------+-----+------------+-----------+--------------+------------+--------+-----------+
7 rows in set (0.00 sec) mysql> select * from employee having salary > 10000;
+----+-----------+--------+-----+------------+-----------+--------------+------------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+-----------+--------+-----+------------+-----------+--------------+------------+--------+-----------+
| 2 | alex | male | 78 | 2015-03-02 | teacher | NULL | 1000000.31 | 401 | 1 |
| 7 | jinxin | male | 18 | 1900-03-01 | teacher | NULL | 30000.00 | 401 | 1 |
| 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 |
+----+-----------+--------+-----+------------+-----------+--------------+------------+--------+-----------+
7 rows in set (0.00 sec) mysql> 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
ERROR 1054 (42S22): Unknown column 'salary' in 'having clause' # 无法直接取到其他字段，可以使用聚合函数
mysql> select post,group_concat(name) from employee group by post having avg(salary) > 10000;
+-----------+---------------------------------------------------------+
| post | group_concat(name) |
+-----------+---------------------------------------------------------+
| operation | 张野,程咬金,程咬银,程咬铜,程咬铁 |
| teacher | alex,wupeiqi,yuanhao,liwenzhou,jingliyang,jinxin,成龙 |
+-----------+---------------------------------------------------------+
2 rows in set (0.00 sec)
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
2. 查询各岗位平均薪资大于10000的岗位名、平均工资
3. 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. 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
# 员工个数过滤前
mysql> select post, group_concat(name), count(id) from employee group by post;
+-----------------------------------------+---------------------------------------------------------+-----------+
| post | group_concat(name) | count(id) |
+-----------------------------------------+---------------------------------------------------------+-----------+
| operation | 张野,程咬金,程咬银,程咬铜,程咬铁 | 5 |
| sale | 歪歪,丫丫,丁丁,星星,格格 | 5 |
| teacher | alex,wupeiqi,yuanhao,liwenzhou,jingliyang,jinxin,成龙 | 7 |
| 老男孩驻沙河办事处外交大使 | egon | 1 |
+-----------------------------------------+---------------------------------------------------------+-----------+
4 rows in set (0.00 sec) # 员工个数过滤后
mysql> select post, group_concat(name), count(id) from employee group by post having count(id) < 2;
+-----------------------------------------+--------------------+-----------+
| post | group_concat(name) | count(id) |
+-----------------------------------------+--------------------+-----------+
| 老男孩驻沙河办事处外交大使 | egon | 1 |
+-----------------------------------------+--------------------+-----------+
1 row in set (0.00 sec) # 2.查询各岗位平均薪资大于10000的岗位名、平均工资
mysql> select post, avg(salary) as avg_salary from employee group by post having avg_salary > 10000;
+-----------+---------------+
| post | avg_salary |
+-----------+---------------+
| operation | 16800.026000 |
| teacher | 151842.901429 |
+-----------+---------------+
2 rows in set (0.00 sec) # 3.查询各岗位平均薪资大于10000且小于20000的岗位名、平均工资
mysql> select post, avg(salary) as avg_salary from employee group by post having avg_salary between 10000 and 20000;
+-----------+--------------+
| post | avg_salary |
+-----------+--------------+
| operation | 16800.026000 |
+-----------+--------------+
1 row in set (0.00 sec)
练习题答案
七、查询排序：ORDER BY
按单列排序：
ORDER BY...： 默认是升序排列
ORDER BY ... ASC：升序排列
ORDER BY ... DESC：降序排列
mysql> select * from employee ORDER BY salary;
+----+------------+--------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
| 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 |
| 10 | 丫丫 | female | 38 | 2010-11-01 | sale | NULL | 2000.35 | 402 | 2 |
| 5 | liwenzhou | male | 28 | 2012-11-01 | teacher | NULL | 2100.00 | 401 | 1 |
| 9 | 歪歪 | female | 48 | 2015-03-11 | sale | NULL | 3000.13 | 402 | 2 |
| 12 | 星星 | female | 18 | 2016-05-13 | sale | NULL | 3000.29 | 402 | 2 |
| 4 | yuanhao | male | 73 | 2014-07-01 | teacher | NULL | 3500.00 | 401 | 1 |
| 13 | 格格 | female | 28 | 2017-01-27 | sale | NULL | 4000.33 | 402 | 2 |
| 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 |
| 3 | wupeiqi | male | 81 | 2013-03-05 | teacher | NULL | 8300.00 | 401 | 1 |
| 6 | jingliyang | female | 18 | 2011-02-11 | teacher | NULL | 9000.00 | 401 | 1 |
| 8 | 成龙 | male | 48 | 2010-11-11 | teacher | NULL | 10000.00 | 401 | 1 |
| 14 | 张野 | male | 28 | 2016-03-11 | operation | NULL | 10000.13 | 403 | 3 |
| 18 | 程咬铁 | female | 18 | 2014-05-12 | operation | NULL | 17000.00 | 403 | 3 |
| 17 | 程咬铜 | male | 18 | 2015-04-11 | operation | NULL | 18000.00 | 403 | 3 |
| 16 | 程咬银 | female | 18 | 2013-03-11 | operation | NULL | 19000.00 | 403 | 3 |
| 15 | 程咬金 | male | 18 | 1997-03-12 | operation | NULL | 20000.00 | 403 | 3 |
| 7 | jinxin | male | 18 | 1900-03-01 | teacher | NULL | 30000.00 | 401 | 1 |
| 2 | alex | male | 78 | 2015-03-02 | teacher | NULL | 1000000.31 | 401 | 1 |
+----+------------+--------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
18 rows in set (0.00 sec) mysql> select * from employee ORDER BY salary ASC;
+----+------------+--------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
| 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 |
| 10 | 丫丫 | female | 38 | 2010-11-01 | sale | NULL | 2000.35 | 402 | 2 |
| 5 | liwenzhou | male | 28 | 2012-11-01 | teacher | NULL | 2100.00 | 401 | 1 |
| 9 | 歪歪 | female | 48 | 2015-03-11 | sale | NULL | 3000.13 | 402 | 2 |
| 12 | 星星 | female | 18 | 2016-05-13 | sale | NULL | 3000.29 | 402 | 2 |
| 4 | yuanhao | male | 73 | 2014-07-01 | teacher | NULL | 3500.00 | 401 | 1 |
| 13 | 格格 | female | 28 | 2017-01-27 | sale | NULL | 4000.33 | 402 | 2 |
| 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 |
| 3 | wupeiqi | male | 81 | 2013-03-05 | teacher | NULL | 8300.00 | 401 | 1 |
| 6 | jingliyang | female | 18 | 2011-02-11 | teacher | NULL | 9000.00 | 401 | 1 |
| 8 | 成龙 | male | 48 | 2010-11-11 | teacher | NULL | 10000.00 | 401 | 1 |
| 14 | 张野 | male | 28 | 2016-03-11 | operation | NULL | 10000.13 | 403 | 3 |
| 18 | 程咬铁 | female | 18 | 2014-05-12 | operation | NULL | 17000.00 | 403 | 3 |
| 17 | 程咬铜 | male | 18 | 2015-04-11 | operation | NULL | 18000.00 | 403 | 3 |
| 16 | 程咬银 | female | 18 | 2013-03-11 | operation | NULL | 19000.00 | 403 | 3 |
| 15 | 程咬金 | male | 18 | 1997-03-12 | operation | NULL | 20000.00 | 403 | 3 |
| 7 | jinxin | male | 18 | 1900-03-01 | teacher | NULL | 30000.00 | 401 | 1 |
| 2 | alex | male | 78 | 2015-03-02 | teacher | NULL | 1000000.31 | 401 | 1 |
+----+------------+--------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
18 rows in set (0.00 sec) mysql> select * from employee ORDER BY salary DESC;
+----+------------+--------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+------------+--------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
| 2 | alex | male | 78 | 2015-03-02 | teacher | NULL | 1000000.31 | 401 | 1 |
| 7 | jinxin | male | 18 | 1900-03-01 | teacher | NULL | 30000.00 | 401 | 1 |
| 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 |
| 14 | 张野 | male | 28 | 2016-03-11 | operation | NULL | 10000.13 | 403 | 3 |
| 8 | 成龙 | male | 48 | 2010-11-11 | teacher | NULL | 10000.00 | 401 | 1 |
| 6 | jingliyang | female | 18 | 2011-02-11 | teacher | NULL | 9000.00 | 401 | 1 |
| 3 | wupeiqi | male | 81 | 2013-03-05 | teacher | NULL | 8300.00 | 401 | 1 |
| 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 |
| 13 | 格格 | female | 28 | 2017-01-27 | sale | NULL | 4000.33 | 402 | 2 |
| 4 | yuanhao | male | 73 | 2014-07-01 | teacher | NULL | 3500.00 | 401 | 1 |
| 12 | 星星 | female | 18 | 2016-05-13 | sale | NULL | 3000.29 | 402 | 2 |
| 9 | 歪歪 | female | 48 | 2015-03-11 | sale | NULL | 3000.13 | 402 | 2 |
| 5 | liwenzhou | male | 28 | 2012-11-01 | teacher | NULL | 2100.00 | 401 | 1 |
| 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 |
+----+------------+--------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
18 rows in set (0.00 sec)
单列排序示例
按多列排序：
上面是按工资排，如果按age排序，有很多人年纪是相同的，这时就需要采用多列排序了。
例如：先按照age升序排，如果age相同按照id降序排
mysql> select * from employee
-> ORDER BY AGE,
-> id DESC;
+----+------------+--------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+------------+--------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
| 18 | 程咬铁 | female | 18 | 2014-05-12 | operation | NULL | 17000.00 | 403 | 3 |
| 17 | 程咬铜 | male | 18 | 2015-04-11 | operation | NULL | 18000.00 | 403 | 3 |
| 16 | 程咬银 | female | 18 | 2013-03-11 | operation | NULL | 19000.00 | 403 | 3 |
| 15 | 程咬金 | male | 18 | 1997-03-12 | operation | NULL | 20000.00 | 403 | 3 |
| 12 | 星星 | female | 18 | 2016-05-13 | sale | NULL | 3000.29 | 402 | 2 |
| 11 | 丁丁 | female | 18 | 2011-03-12 | sale | NULL | 1000.37 | 402 | 2 |
| 7 | jinxin | male | 18 | 1900-03-01 | teacher | NULL | 30000.00 | 401 | 1 |
| 6 | jingliyang | female | 18 | 2011-02-11 | teacher | NULL | 9000.00 | 401 | 1 |
| 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 |
| 14 | 张野 | male | 28 | 2016-03-11 | operation | NULL | 10000.13 | 403 | 3 |
| 13 | 格格 | female | 28 | 2017-01-27 | sale | NULL | 4000.33 | 402 | 2 |
| 5 | liwenzhou | male | 28 | 2012-11-01 | teacher | NULL | 2100.00 | 401 | 1 |
| 10 | 丫丫 | female | 38 | 2010-11-01 | sale | NULL | 2000.35 | 402 | 2 |
| 9 | 歪歪 | female | 48 | 2015-03-11 | sale | NULL | 3000.13 | 402 | 2 |
| 8 | 成龙 | male | 48 | 2010-11-11 | teacher | NULL | 10000.00 | 401 | 1 |
| 4 | yuanhao | male | 73 | 2014-07-01 | teacher | NULL | 3500.00 | 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 |
+----+------------+--------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
18 rows in set (0.00 sec)
有order by的sql语句，执行顺序（注意与语法顺序的异同）：
先执行from找到表；再按照where约束条件过滤数据；再交给group by进行分组；接着交给having进行过滤；
过滤之后运行distinct进行去重（没有distinct就不去重）；去重之后再执行order by进行排序；orderby 运行完之后运行limit。
最需要注意的一点：where这一步的时候还没有分组，因此where不能用聚合函数。体会下面这个用例
mysql> select * from employee where max(salary) > 1000;
ERROR 1111 (HY000): Invalid use of group function
mysql> select max(salary) from employee where salary > 1000;
+-------------+
| max(salary) |
+-------------+
| 1000000.31 |
+-------------+
1 row in set (0.00 sec)
另一个关注的重点：distinct语句执行是在having后面。体会下面这个用例：(用例实际执行和教材不同，需关注)
having不能使用distinct定义的别名，order by 则可以使用。
mysql> select post, count(id) as emp_count from employee
-> where salary > 1000
-> group by post
-> having emp_count > 5; # 此处引用不了emp_count别名，因为distinct还没有执行
+---------+-----------+
| post | emp_count |
+---------+-----------+
| teacher | 7 |
+---------+-----------+
1 row in set (0.00 sec) mysql> select post, count(id) as emp_count from employee where salary > 1000 group by post having count(id) > 5;
+---------+-----------+
| post | emp_count |
+---------+-----------+
| teacher | 7 |
+---------+-----------+
1 row in set (0.00 sec)
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. 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
mysql> select * from employee ORDER BY age ASC, hire_date DESC;
+----+------------+--------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
| 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 |
| 12 | 星星 | female | 18 | 2016-05-13 | sale | NULL | 3000.29 | 402 | 2 |
| 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 |
| 16 | 程咬银 | female | 18 | 2013-03-11 | operation | NULL | 19000.00 | 403 | 3 |
| 11 | 丁丁 | female | 18 | 2011-03-12 | sale | NULL | 1000.37 | 402 | 2 |
| 6 | jingliyang | female | 18 | 2011-02-11 | teacher | NULL | 9000.00 | 401 | 1 |
| 15 | 程咬金 | male | 18 | 1997-03-12 | operation | NULL | 20000.00 | 403 | 3 |
| 7 | jinxin | male | 18 | 1900-03-01 | teacher | NULL | 30000.00 | 401 | 1 |
| 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 |
| 5 | liwenzhou | male | 28 | 2012-11-01 | teacher | NULL | 2100.00 | 401 | 1 |
| 10 | 丫丫 | female | 38 | 2010-11-01 | sale | NULL | 2000.35 | 402 | 2 |
| 9 | 歪歪 | female | 48 | 2015-03-11 | sale | NULL | 3000.13 | 402 | 2 |
| 8 | 成龙 | male | 48 | 2010-11-11 | teacher | NULL | 10000.00 | 401 | 1 |
| 4 | yuanhao | male | 73 | 2014-07-01 | teacher | NULL | 3500.00 | 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 |
+----+------------+--------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
18 rows in set (0.00 sec) # 分组之后，distinct这里只能查被分组的字段和聚合函数
# 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
mysql> select post, avg(salary),group_concat(name) from employee GROUP BY post having avg(salary) > 10000 order by avg(salary) ASC;
+-----------+---------------+---------------------------------------------------------+
| post | avg(salary) | group_concat(name) |
+-----------+---------------+---------------------------------------------------------+
| operation | 16800.026000 | 张野,程咬金,程咬银,程咬铜,程咬铁 |
| teacher | 151842.901429 | alex,wupeiqi,yuanhao,liwenzhou,jingliyang,jinxin,成龙 |
+-----------+---------------+---------------------------------------------------------+
2 rows in set (0.00 sec) # 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
mysql> select post, avg(salary),group_concat(name) from employee GROUP BY post having avg(salary) > 10000 order by avg(salary) DESC;
+-----------+---------------+---------------------------------------------------------+
| post | avg(salary) | group_concat(name) |
+-----------+---------------+---------------------------------------------------------+
| teacher | 151842.901429 | alex,wupeiqi,yuanhao,liwenzhou,jingliyang,jinxin,成龙 |
| operation | 16800.026000 | 张野,程咬金,程咬银,程咬铜,程咬铁 |
+-----------+---------------+---------------------------------------------------------+
2 rows in set (0.00 sec)
练习题答案
八、限制查询的记录数：LIMIT
LIMIT语法上是写在最后，执行时也是最后一个执行。
限制最终打印在屏幕上的条数。
mysql> select * from employee order by salary desc
-> limit 3;
+----+-----------+------+-----+------------+-----------+--------------+------------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+-----------+------+-----+------------+-----------+--------------+------------+--------+-----------+
| 2 | alex | male | 78 | 2015-03-02 | teacher | NULL | 1000000.31 | 401 | 1 |
| 7 | jinxin | male | 18 | 1900-03-01 | teacher | NULL | 30000.00 | 401 | 1 |
| 15 | 程咬金 | male | 18 | 1997-03-12 | operation | NULL | 20000.00 | 403 | 3 |
+----+-----------+------+-----+------------+-----------+--------------+------------+--------+-----------+
3 rows in set (0.00 sec) # 找出工资最高人的详细信息
mysql> select * from employee order by salary desc limit 1;
+----+------+------+-----+------------+---------+--------------+------------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+------+------+-----+------------+---------+--------------+------------+--------+-----------+
| 2 | alex | male | 78 | 2015-03-02 | teacher | NULL | 1000000.31 | 401 | 1 |
+----+------+------+-----+------------+---------+--------------+------------+--------+-----------+
1 row in set (0.00 sec)
LIMIT还能够实现分页功能（但是使用LIMIT来分页效率不高，一般还是需要一些缓存机制来帮忙实现分页）
# limit做分页功能
mysql> select * from employee order by salary DESC
-> limit 0,5;
+----+-----------+--------+-----+------------+-----------+--------------+------------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+-----------+--------+-----+------------+-----------+--------------+------------+--------+-----------+
| 2 | alex | male | 78 | 2015-03-02 | teacher | NULL | 1000000.31 | 401 | 1 |
| 7 | jinxin | male | 18 | 1900-03-01 | teacher | NULL | 30000.00 | 401 | 1 |
| 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 |
+----+-----------+--------+-----+------------+-----------+--------------+------------+--------+-----------+
5 rows in set (0.01 sec) mysql> 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
+----+------------+--------+-----+------------+-----------+--------------+----------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+------------+--------+-----+------------+-----------+--------------+----------+--------+-----------+
| 18 | 程咬铁 | female | 18 | 2014-05-12 | operation | NULL | 17000.00 | 403 | 3 |
| 14 | 张野 | male | 28 | 2016-03-11 | operation | NULL | 10000.13 | 403 | 3 |
| 8 | 成龙 | male | 48 | 2010-11-11 | teacher | NULL | 10000.00 | 401 | 1 |
| 6 | jingliyang | female | 18 | 2011-02-11 | teacher | NULL | 9000.00 | 401 | 1 |
| 3 | wupeiqi | male | 81 | 2013-03-05 | teacher | NULL | 8300.00 | 401 | 1 |
+----+------------+--------+-----+------------+-----------+--------------+----------+--------+-----------+
5 rows in set (0.00 sec)
limit来实现分页显示
九、正则查询
更加强大的模糊匹配——正则表达式。
调用正则表达式查询的关键字——REGEXP
# 名字是'jin'开头的记录
mysql> select * from employee where name regexp '^jin';
+----+------------+--------+-----+------------+---------+--------------+----------+--------+-----------+
| 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 |
+----+------------+--------+-----+------------+---------+--------------+----------+--------+-----------+
2 rows in set (0.01 sec) # 名字是'jin'开头，且以g或n结尾的记录
mysql> select * from employee where name regexp '^jin.*(g|n)$';
+----+------------+--------+-----+------------+---------+--------------+----------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+------------+--------+-----+------------+---------+--------------+----------+--------+-----------+
| 6 | jingliyang | female | 18 | 2011-02-11 | teacher | NULL | 9000.00 | 401 | 1 |
| 7 | jinxin | male | 18 | 1900-03-01 | teacher | NULL | 30000.00 | 401 | 1 |
+----+------------+--------+-----+------------+---------+--------------+----------+--------+-----------+
2 rows in set (0.00 sec) # 名字以on结尾的记录
mysql> select * from employee where name regexp 'on$';
+----+------+------+-----+------------+-----------------------------------------+--------------+---------+--------+-----------+
| 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 |
+----+------+------+-----+ # 匹配m字符两次'mm'
mysql> select * from employee where name regexp 'm{2}';
Empty set (0.00 sec) mysql> select * from employee where name regexp 'g{1}';
+----+------------+--------+-----+------------+-----------------------------------------+--------------+---------+--------+-----------+
| 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 |
| 6 | jingliyang | female | 18 | 2011-02-11 | teacher | NULL | 9000.00 | 401 | 1 |
+----+------------+--------+-----+------------+-----------------------------------------+--------------+---------+--------+-----------+
2 rows in set (0.00 sec)
正则表达式使用示例
小结：对字符串匹配的方式
WHERE name = 'egon';
WHERE name LIKE 'yua%';
WHERE name REGEXP 'on$';
十、单表查询的语法顺序和执行顺序总结
语法顺序：
select distinct 字段1,字段2,字段3 from 库.表
where 条件
group by 分组条件
having 过滤
order by 排序字段
limit n;
执行顺序：
select执行了一个打印，各个关键字关系用伪代码表示如下：
def from(db, table):
f = open(r'%s\%s' %(db, table))
return f def where(condition, f):
for line in f:
if condition:
yield line def group(lines):
pass def having(group_res):
pass def distinct(having_res):
pass def order(distinct_res):
pass def limit(order_res):
pass def select():
from('db1', 't1')
lines=where('id>3',f)
group_res=group(lines)
having_res=having(group_res)
distinct_res=distinct(having_res)
order_res=order(distinct_res)
res=limit(order_res)
print(res)
return res
执行顺序伪代码