记录相关操作
插入数据
1. 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);
2. 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…);
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);
4. 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 …;
更新数据
语法：
UPDATE 表名 SET
字段1=值1,
字段2=值2,
WHERE CONDITION;
示例：
UPDATE mysql.user SET password=password(‘123’)
where user=’root’ and host=’localhost’;
删除数据
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
语法
select distinct 字段 from 库.表
where 过滤条件
group by 分组字段
having 过滤条件
order by 排序条件
limit 条数
#优先级排序
from
where
group by
having
select
distinct
order by
limit
环境准备
#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
#三个部门：教学，销售，运营
insert into employee(name,sex,age,hire_date,post,salary,office,depart_id) values
('egon','male',18,'20170301','老男孩驻沙河办事处外交大使',7300.33,401,1), #以下是教学部
('alex','male',78,'20150302','teacher',1000000.31,401,1),
('wupeiqi','male',81,'20130305','teacher',8300,401,1),
('yuanhao','male',73,'20140701','teacher',3500,401,1),
('liwenzhou','male',28,'20121101','teacher',2100,401,1),
('jingliyang','female',18,'20110211','teacher',9000,401,1),
('jinxin','male',18,'19000301','teacher',30000,401,1),
('成龙','male',48,'20101111','teacher',10000,401,1),
('歪歪','female',48,'20150311','sale',3000.13,402,2),#以下是销售部门
('丫丫','female',38,'20101101','sale',2000.35,402,2),
('丁丁','female',18,'20110312','sale',1000.37,402,2),
('星星','female',18,'20160513','sale',3000.29,402,2),
('格格','female',28,'20170127','sale',4000.33,402,2),
('张野','male',28,'20160311','operation',10000.13,403,3), #以下是运营部门
('程咬金','male',18,'19970312','operation',20000,403,3),
('程咬银','female',18,'20130311','operation',19000,403,3),
('程咬铜','male',18,'20150411','operation',18000,403,3),
('程咬铁','female',18,'20140512','operation',17000,403,3)
;
简单查询
#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 "年薪" from employee;
select name,salary*12 "年薪" from employee;
#定义显示格式
CONCAT() 函数用于连接字符串
select concat("姓名：",name) as "姓名" , concat("年薪:",salary*12) "年薪" 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
employee;
where约束
可以使用的
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
使用方法
#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;
# 等价
select name,salary from employee where salary >= 10000 and salary <= 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__';
#7：正则匹配查找
regexp
select * from employee where name regexp '^jin';
select * from employee where name regexp 'n$';
select * from employee where name regexp '^jin|n$|g$';
group by
为什么要分组，查询的时候使用，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
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
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;
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
聚合函数
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;
group by 与聚合函数案例
# 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) from employee group by sex;
# 查询岗位名以及各岗位的最低薪资
select post,min(salary) from employee group by post;
# 查询岗位名以及各岗位的最高薪资
select post,max(salary) from employee group by post;
# 查询岗位名以及各岗位的平均薪资
select post,avg(salary) from employee group by post;
# 查询公司内男员工和女员工的个数
select sex,count(*) from employee group by sex;
# 查询岗位名以及各岗位内包含的员工个数
select post,count(name) 个数 from employee group by post;
# 查询岗位名以及岗位包含的所有员工名字
select post,group_concat(name) from employee group by post;
having过滤
#！！！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
# 简而言之，having用在group by后面
案例
# 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,count(name) count from employee group by post having count < 2;
# 查询各岗位平均薪资大于10000的岗位名、平均工资
select post,avg(salary) avg_salary from employee group by post having avg_salary > 10000;
# 查询各岗位平均薪资大于10000且小于20000的岗位名、平均工资
select post,avg(salary) avg_salary from employee group by post having avg_salary between 10000 and 20000;
order by
排序查询
语法
按单列排序
SELECT * FROM employee ORDER BY salary; # 默认升序
SELECT * FROM employee ORDER BY salary ASC; # 指定升序
SELECT * FROM employee ORDER BY salary DESC; # 指定降序
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;
案例
# 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;
# 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
select post,avg(salary) avg_salary from employee group by post having avg_salary>10000 order by avg_salary;#默认升序
# 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
select post,avg(salary) avg_salary from employee group by post having avg_salary>10000 order by avg_salary desc;
limit
限制查询记录数
语法
示例：
SELECT * FROM employee ORDER BY salary DESC
LIMIT 3; #默认初始位置为0
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