数据库03: 表记录操作与查询
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概述
在mysql管理软件中，可以通过SQL语句中的 DML语言来实现数据的操作，包括:
INSERT实现数据的插入;UPDATE实现数据的更新;DELETE实现数据的删除;SELECT查询数据.
INSERT
# 插入完整数据（顺序插入）
语法一：
INSERT INTO 表名(字段1,字段2,字段3…字段n) VALUES(值1,值2,值3…值n);
语法二：
INSERT INTO 表名 VALUES (值1,值2,值3…值n);
# 指定字段插入数据
语法：
INSERT INTO 表名(字段1,字段2,字段3…) VALUES (值1,值2,值3…);
# 插入多条记录
语法：
INSERT INTO 表名 VALUES
(值1,值2,值3…值n),
(值1,值2,值3…值n),
(值1,值2,值3…值n);
# 插入查询结果
语法：
INSERT INTO 表名(字段1,字段2,字段3…字段n)
SELECT (字段1,字段2,字段3…字段n) FROM 表2
WHERE …;UPDATE
UPDATE 表名 SET
字段1=值1,
字段2=值2 WHERE 条件;
# 示例：
UPDATE mysql.user SET password=password(‘123’)
where user=’root’ and host=’localhost’;
DELETE
语法：
DELETE FROM 表名
WHERE CONITION;
示例：
DELETE FROM mysql.user
WHERE password=’’;
练习：
更新MySQL root用户密码为mysql123
删除除从本地登录的root用户以外的所有用户
单表查询
SELECT 字段1,字段2... FROM 表名
WHERE 条件
GROUP BY field
HAVING 筛选
ORDER BY field
LIMIT 限制条数执行优先级(重点)
由上到下, 按顺序执行, 没有就跳过:
where: 约束条件;group by: 分组;having: 过滤;select: ...;distinct: 去重;order by: 排序;limit: 显示条数;
步骤:
- 找到表:
from table_name; - 拿着
where指定的约束条件，去文件/表中取出一条条记录; - 将取出的一条条记录进行分组
group by，如果没有group by，则整体作为一组; - 将分组的结果进行
having过滤; - 执行
select; distinct去重;- 将结果按条件排序：
order by - 限制结果的显示条数:
limit
准备表和记录
# company.employee 表结构
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
);
# 插入记录
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),
('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),
('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),
('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
# 查询所有数据
SELECT * FROM employee;
# 查询特定字段类的数据
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; # 重新命名
SELECT name, salary*12 Annual_salary FROM employee; # 重新命名
# 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;
# 练习
1. 查出所有员工的名字，薪资,格式为: <名字:egon> <薪资:3000>
select concat('<名字', name,'>', ' <薪资', salary, '>') from employee;
2. 查出所有的岗位（去掉重复）
select distinct post from employee;
3. 查出所有员工名字，以及他们的年薪,年薪的字段名为annual_year
select name, salary*12 as annual_salary from employee;WHERE
- 比较运算符：
>,<,>=,<=,<>,!=; between 80 and 100值在80到100之间;in(80,90,100)值是10或20或30;like ‘egon%‘:pattern可以是%或_,%表示任意多字符,_表示一个字符;- 逻辑运算符：在多个条件直接可以使用逻辑运算符
and,or,not;
# 单条件查询
SELECT name FROM employee WHERE post='sale';
# 多条件查询
SELECT name,salary FROM employee
WHERE post='teacher' AND salary>10000;
# BETWEEN num1 AND num2
SELECT name,salary FROM employee
WHERE salary BETWEEN 10000 AND 20000;
SELECT name,salary FROM employee
WHERE salary NOT BETWEEN 10000 AND 20000;
# 判断字段< 10000或者> 20000
# 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
# or, 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) ;
# 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;
select name, age from employee where post='teacher';
2. 查看岗位是teacher且年龄大于30岁的员工姓名、年龄;
select name, age from employee where post='teacher' and age>30;
3. 查看岗位是teacher且薪资在9000-10000范围内的员工姓名、年龄、薪资;
select name, age, salary from employee
where post='teacher' and salary between 9000 and 10000;
4. 查看岗位描述不为NULL的员工信息;
select id, post from employee where post_comment is not null;
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;
select name, age, salary from employee
where post='teacher' and salary in (10000,9000,30000);
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;
select name, age, salary from employee
where post='teacher' and salary not in (10000,9000,30000);
7. 查看岗位是teacher且名字是jin开头的员工姓名、年薪;
select name,salary*12 as annual_salary from employee
where post='teacher' and name like 'jin%';GROUP BY
- 分组发生在关键字
where约束之后，即分组是基于where之后得到的记录而进行的; - 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，或者按照性别进行分组等;
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
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;
# GROUP BY: 单独使用
SELECT post FROM employee GROUP BY post;
# GROUP BY & GROUP_CONCAT() 组合使用
# 按照岗位分组，并连接组内成员姓名
SELECT post,GROUP_CONCAT(name) as emp_members FROM employee GROUP BY post;
# GROUP BY & 聚合函数 组合使用
# 按照岗位分组，并查看每个组有多少人
select post,count(id) as count from employee group by post;
# 求每个分类的记录个数
select depart_id,count(name) from employee group by depart_id;
+-----------+-------------+
| depart_id | count(name) |
+-----------+-------------+
| 1 | 8 |
| 2 | 5 |
| 3 | 5 |
+-----------+-------------+
3 rows in set (0.00 sec)
# 将符合类别的所有记录的名字组合成一项
select depart_id, group_concat(name) from employee
group by depart_id;
# 求每个部门中的工资的最大值
select depart_id, max(salary) from employee group by depart_id;
+-----------+-------------+
| depart_id | max(salary) |
+-----------+-------------+
| 1 | 1000000.31 |
| 2 | 3000.29 |
| 3 | 20000.00 |
+-----------+-------------+
3 rows in set (0.00 sec)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
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;
# 练习
1. 查询 岗位名 以及 岗位包含的所有员工名字
select post, group_concat(name) from emp group by post;
2. 查询岗位名以及各岗位内包含的员工个数
select post, count(id) from emp group by post;
3. 查询公司内男员工和女员工的个数
select sex, count(id) from emp group by sex;
4. 查询岗位名以及各岗位的平均薪资
select post, avg(salary) as '平均薪资' from emp group by post;
5. 查询岗位名以及各岗位的最高薪资
select post, max(salary) as '最高薪资' from emp group by post;
6. 查询岗位名以及各岗位的最低薪资
select post, max(salary) as '最低薪资' from emp group by post;
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
select sex, avg(salary) as '平均薪资' from emp group by sex;HAVING
Having条件在group by之后执行，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.
# 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
select post, group_concat(name) as emp_names, count(id) as emp_num from employee group by post having emp_num <2;
3. 查询每个岗位 平均薪资大于10000 的岗位名、平均工资
select post, avg(salary) as avg_salary from employee
group by post having avg_salary>10000;
4. 查询每个岗位 平均薪资大于10000 且 小于20000的岗位名、平均工资
select post, avg(salary) from emp group by post
having avg(salary) in (10000, 20000) ;ORDER BY
# 按单列排序, 默认升序
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;
# 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:
select * from employee order by age, hire_date desc;
2. 查询每个岗位 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:
select post, avg(salary) as post_avg from employee
group by post having post_avg>10000 order by post_avg;limit
限定查询结果记录的条数;
索引默认从0开始;
limit 0, 2: 从索引0开始, 然后长度是2;
SELECT * FROM employee ORDER BY salary DESC
LIMIT 3;
SELECT * FROM employee ORDER BY salary DESC
LIMIT 0,5;
SELECT * FROM employee ORDER BY salary DESC
LIMIT 5,5;
# 练习
1. 分页显示，每页5条
select * from emp limit 5;
select * from emp limit 5, 5;
select * from emp limit 10, 5;
正则表达式查询
SELECT * FROM employee WHERE name REGEXP '^ale';
SELECT * FROM employee WHERE name REGEXP 'on$';
SELECT * FROM employee WHERE name REGEXP 'm{2}';
小结：对字符串匹配的方式
WHERE name = 'egon'; # 准确查询
WHERE name LIKE 'yua%'; # 模糊查询
WHERE name REGEXP 'on$'; # 模糊查询
# 练习
查看所有员工中名字是jin开头，n或者g结果的员工信息
select * from emp where name regexp "^jin.*[ng]$";
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