2.8单表查询
"单表查询语法顺序"
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;
"单标查询的执行顺序"
2.8.1准备表和数据
#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','大使Post',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)
;
#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;
mysql> select distinct post from employee;
+-----------------------------------------+
| post |
+-----------------------------------------+
| 大使Post |
| teacher |
| sale |
| operation |
+-----------------------------------------+
4 rows in set (0.00 sec)
#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;
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 |
# 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;
mysql> select CONCAT('姓名:',name,' 工资:',salary) from employee where post='sale';
+------------------------------------------+
| CONCAT('姓名:',name,' 工资:',salary) |
+------------------------------------------+
| 姓名:歪歪 工资:3000.13 |
| 姓名:丫丫 工资:2000.35 |
| 姓名:丁丁 工资:1000.37 |
| 姓名:星星 工资:3000.29 |
| 姓名:格格 工资:4000.33 |
+------------------------------------------+
5 rows in set (0.00 sec)
mysql>
"CONCAT_WS() 第一个参数为分隔符"
SELECT CONCAT_WS(':',name,salary*12) AS Annual_salary
FROM employee;
mysql> select CONCAT_WS(':',name,salary*12) from employee where post='sale';
+-------------------------------+
| CONCAT_WS(':',name,salary*12) |
+-------------------------------+
| 歪歪:36001.56 |
| 丫丫:24004.20 |
| 丁丁:12004.44 |
| 星星:36003.48 |
| 格格:48003.96 |
+-------------------------------+
5 rows in set (0.00 sec)
mysql>
2.8.2where约束
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 'egon%'
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 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__';
"练习"
1. 查看岗位是teacher的员工姓名、年龄
mysql> select name,age from employee where post='teacher'
-> ;
+------------+-----+
| name | age |
+------------+-----+
| alex | 78 |
| wupeiqi | 81 |
| yuanhao | 73 |
| liwenzhou | 28 |
| jingliyang | 18 |
| jinxin | 18 |
| 成龙 | 48 |
+------------+-----+
7 rows in set (0.00 sec)
2. 查看岗位是teacher且年龄大于30岁的员工姓名、年龄
mysql> select name,age from employee where post='teacher' and age > 30;
+---------+-----+
| name | age |
+---------+-----+
| alex | 78 |
| wupeiqi | 81 |
| yuanhao | 73 |
| 成龙 | 48 |
+---------+-----+
4 rows in set (0.01 sec)
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
mysql> select name,age,salary from employee where post='teacher' and salary between 1000 and 9000;;
+------------+-----+---------+
| name | age | salary |
+------------+-----+---------+
| wupeiqi | 81 | 8300.00 |
| yuanhao | 73 | 3500.00 |
| liwenzhou | 28 | 2100.00 |
| jingliyang | 18 | 9000.00 |
+------------+-----+---------+
4 rows in set (0.00 sec)
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 | |
+--------------+-----------------------+------+-----+---------+----------------+
10 rows in set (0.00 sec)
4. 查看岗位描述不为NULL的员工信息
mysql> select * from employee where post_comment is not null;
Empty set (0.01 sec)
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 | 大使Post | 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)
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
mysql> select name,age,salary from employee where salary in (10000,90000,30000)
-> ;
+--------+-----+----------+
| name | age | salary |
+--------+-----+----------+
| jinxin | 18 | 30000.00 |
| 成龙 | 48 | 10000.00 |
+--------+-----+----------+
2 rows in set (0.01 sec)
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
mysql> select name,age,salary from employee where post='teacher' and salary not in (9000,10000,30000);
+-----------+-----+------------+
| name | age | salary |
+-----------+-----+------------+
| alex | 78 | 1000000.31 |
| wupeiqi | 81 | 8300.00 |
| yuanhao | 73 | 3500.00 |
| liwenzhou | 28 | 2100.00 |
+-----------+-----+------------+
4 rows in set (0.00 sec)
7. 查看岗位是teacher且名字是jin开头的员工姓名、年薪
mysql> select * from employee where name like '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 (0.00 sec)
mysql>
2.8.3group by
#1、首先明确一点：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、为何要分组呢？
取每个部门的最高工资
取每个部门的员工数
取男人数和女人数
小窍门：‘每’这个字后面的字段，就是我们分组的依据
#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
"ONLY_FULL_GROUP_BY"
在ONLY_FULL_GROUP_BY模式下，select 的列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。
mysql> select @@global.sql_mode;
+-------------------+
| @@global.sql_mode |
+-------------------+
| |
+-------------------+
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 |
+----+------+--------+-----+------------+----------------------------+--------------+------------+--------+-----------+
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> select @@global.sql_mode;
+--------------------+
| @@global.sql_mode |
+--------------------+
| ONLY_FULL_GROUP_BY |
+--------------------+
1 row in set (0.00 sec)
mysql>
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 |
| 大使Post| 1 |
+----------------------------+-----------+
rows in set (0.00 sec)
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，需要借助聚合函数
GROUP BY关键字和GROUP_CONCAT()函数一起使用
SELECT post,GROUP_CONCAT(name) FROM employee GROUP BY post;#按照岗位分组，并查看组内成员名
SELECT post,GROUP_CONCAT(name) as emp_members FROM employee GROUP BY post;
mysql> select post,group_concat(name) as emp_name from employee group by post;
+------------+---------------------------------------------------------+
| post | emp_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 |
| 大使Post | egon |
+------------+---------------------------------------------------------+
4 rows in set (0.01 sec)
mysql>
GROUP BY与聚合函数一起使用
select post,count(id) as count from employee group by post;#按照岗位分组，并查看每个组有多少人
"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"
2.8.4聚合函数
#强调：聚合函数聚合的是组的内容，若是没有分组，则默认一组
示例：
SELECT COUNT(*) FROM employee;
SELECT COUNT(*) FROM employee WHERE depart_id=1;
SELECT MAX(salary) FROM employee;
SELECT MIN(salary) FROM employee;
SELECT AVG(salary) FROM employee;
SELECT SUM(salary) FROM employee;
SELECT SUM(salary) FROM employee WHERE depart_id=3;
1. 查询岗位名以及岗位包含的所有员工名字
mysql> select post,group_concat(name) from employee 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 |
| 大使Post | egon |
+------------+---------------------------------------------------------+
4 rows in set (0.00 sec)
mysql>
2. 查询岗位名以及各岗位内包含的员工个数
mysql> select post,count(name) from employee group by post;
+------------+-------------+
| post | count(name) |
+------------+-------------+
| operation | 5 |
| sale | 5 |
| teacher | 7 |
| 大使Post | 1 |
+------------+-------------+
4 rows in set (0.00 sec)
mysql>
3. 查询公司内男员工和女员工的个数
mysql> select sex,count(*) from employee group by sex;
+--------+----------+
| sex | count(*) |
+--------+----------+
| male | 10 |
| female | 8 |
+--------+----------+
2 rows in set (0.00 sec)
mysql>
4. 查询岗位名以及各岗位的平均薪资
mysql> select post,avg(salary) from employee group by post;
+------------+---------------+
| post | avg(salary) |
+------------+---------------+
| operation | 16800.026000 |
| sale | 2600.294000 |
| teacher | 151842.901429 |
| 大使Post | 7300.330000 |
+------------+---------------+
4 rows in set (0.00 sec)
mysql>
5. 查询岗位名以及各岗位的最高薪资
mysql> select post,max(salary) from employee group by post;
+------------+-------------+
| post | max(salary) |
+------------+-------------+
| operation | 20000.00 |
| sale | 4000.33 |
| teacher | 1000000.31 |
| 大使Post | 7300.33 |
+------------+-------------+
4 rows in set (0.00 sec)
mysql>
6. 查询岗位名以及各岗位的最低薪资
mysql> select post,min(salary) from employee group by post;
+------------+-------------+
| post | min(salary) |
+------------+-------------+
| operation | 10000.13 |
| sale | 1000.37 |
| teacher | 2100.00 |
| 大使Post | 7300.33 |
+------------+-------------+
4 rows in set (0.00 sec)
mysql>
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
mysql> select sex,avg(salary) from employee group by sex;
+--------+---------------+
| sex | avg(salary) |
+--------+---------------+
| male | 110920.077000 |
| female | 7250.183750 |
+--------+---------------+
2 rows in set (0.00 sec)
mysql>
2.8.5having
#！！！执行优先级从高到低：where > group by > having
#1. Where 发生在分组group by之前，因而Where中可以有任意字段，但是绝对不能使用聚合函数。
#2. Having发生在分组group by之后，因而Having中可以使用分组的字段，无法直接取到其他字段,可以使用聚合函数
"验证"
mysql> select @@sql_mode;
+--------------------+
| @@sql_mode |
+--------------------+
| ONLY_FULL_GROUP_BY |
+--------------------+
row in set (0.00 sec)
mysql> select * from emp where salary > 100000;
+----+------+------+-----+------------+---------+--------------+------------+--------+-----------+
| 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 |
+----+------+------+-----+------------+---------+--------------+------------+--------+-----------+
row in set (0.00 sec)
mysql> select * from emp having salary > 100000;
ERROR 1463 (42000): Non-grouping field 'salary' is used in HAVING clause
mysql> select post,group_concat(name) from emp group by post having salary > 10000;#错误，分组后无法直接取到salary字段
ERROR 1054 (42S22): Unknown column 'salary' in 'having clause'
mysql> select post,group_concat(name) from emp group by post having avg(salary) > 10000;
+-----------+-------------------------------------------------------+
| post | group_concat(name) |
+-----------+-------------------------------------------------------+
| operation | 程咬铁,程咬铜,程咬银,程咬金,张野 |
| teacher | 成龙,jinxin,jingliyang,liwenzhou,yuanhao,wupeiqi,alex |
+-----------+-------------------------------------------------------+
rows in set (0.00 sec)
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 post,group_concat(name) from employee group by post having count(*)<2;
+------------+--------------------+
| post | group_concat(name) |
+------------+--------------------+
| 大使Post | egon |
+------------+--------------------+
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) 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)
mysql>
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) 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)
mysql>
2.8.6order by
按单列排序
SELECT * FROM employee ORDER BY salary;
SELECT * FROM employee ORDER BY salary ASC;升序
SELECT * FROM employee ORDER BY salary DESC;降序
按多列排序:先按照age排序，如果年纪相同，则按照薪资排序
SELECT * from employee
ORDER BY age,
salary DESC;
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
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 | 大使Post | 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)
mysql>
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) as 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 |
+-----------+---------------+
2 rows in set (0.00 sec)
mysql>
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> mysql> select post,avg(salary) as avg_salary from employee group by post having avg(salary order by avg_salary desc;
+-----------+---------------+
| post | avg_salary |
+-----------+---------------+
| teacher | 151842.901429 |
| operation | 16800.026000 |
+-----------+---------------+
2 rows in set (0.00 sec)
mysql>
2.8.7sql语句的执行顺序验证
"这里只能order by select的几个列，即 post,avg(salary) as avg_salary，因为代码的执行顺序"
mysql> select post,avg(salary) as avg_salary from employee group by post having avg(salary)>10000 order by id desc;
ERROR 1055 (42000):db1.employee.id isnt in GROUP BY
"因为select的几个列即 post,avg(salary) as avg_salary 还没执行到，所以不能再having里使用列的别名"
mysql> select post,avg(salary) as avg_salary from employee group by post having avg_salary>10000;
ERROR 1463 (42000): Non-grouping field 'avg_salary' is used in HAVING clause
2.8.8limit
示例：
SELECT * FROM employee ORDER BY salary DESC
LIMIT 3; #默认初始位置为0 ,共取三条
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
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 | 大使Post | 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 |
+----+-----------+------+-----+------------+------------+--------------+------------+--------+-----------+
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>
2.8.9正则表达式查询
SELECT * FROM employee WHERE name REGEXP '^ale';
SELECT * FROM employee WHERE name REGEXP 'on$';
SELECT * FROM employee WHERE name REGEXP 'm{2}';
小结：对字符串匹配的方式
WHERE name = 'egon';
WHERE name LIKE 'yua%';
WHERE name REGEXP 'on$';
mysql> select * from employee where name REGEXP '^a';
+----+------+------+-----+------------+---------+--------------+------------+--------+-----------+
| 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 (0.01 sec)
mysql>
