mysql的使用

-- 数据库的操作

-- 链接数据库
mysql -uroot -p
mysql -uroot -pmysql

-- 退出数据库
exit/quit/ctrl+d

-- sql语句最后需要有分号;结尾
-- 显示数据库版本
select version();

-- 显示时间
select now();

-- 查看所有数据库
show databases;

-- 创建数据库
-- create database 数据库名 charset=utf8;
create database python04;
create database python04new charset=utf8;

-- 查看创建数据库的语句
-- show crate database ....
show create database python04;

-- 查看当前使用的数据库
select database();

-- 使用数据库
-- use 数据库的名字
use python04new;

-- 删除数据库
-- drop database 数据库名;
drop database python04;

-- 数据表的操作

-- 查看当前数据库中所有表
show tables;

-- 创建表
-- auto_increment表示自动增长
-- not null 表示不能为空
-- primary key 表示主键s
-- default 默认值
-- create table 数据表名字 (字段 类型 约束[, 字段 类型 约束]);
create table xxxxx(

　　id int, name varchar(30)

);

create table yyyyy(

　　id int primary key not null auto_increment,

　　name varchar(30)

);

create table zzzzz(
　　id int primary key not null auto_increment,
　　name varchar(30)
);

-- 查看表结构
-- desc 数据表的名字;
desc xxxxx;

-- 创建students表(id、name、age、high、gender、cls_id)
create table students(
　　id int unsigned not null auto_increment primary key,
　　name varchar(30),
　　age tinyint unsigned default 0,
　　high decimal(5,2),
　　gender enum("男", "女", "中性", "保密") default "保密",
　　cls_id int unsigned
);

insert into students values(0, "老王", 18, 188.88, "男", 0);
insert into students values(0, "王小二", 19, 150.12, "女", 1);
insert into students values(0, "李爽", 22, 165.00, "女", 2);
insert into students values(0, "李杰", 60, 158.10, "男", 3);
insert into students values(0, "刘菲菲", 12, 175.50, "女", 4);
insert into students values(0, "小明", 19, 161.30, "男", 0);
insert into students values(0, "李蕾", 16, 158.20, "女", 1);
insert into students values(0, "韩没灭", 25, 150.00, "男", 2);
insert into students values(0, "杰克", 36, 180.12, "女", 3);
insert into students values(0, "路西", 18, 183.12, "男", 4);
insert into students values(0, "王静", 12, 196.12, "中性", 1);
insert into students values(0, "王姐", 34, 188.12, "男", 1);
insert into students values(0, "徐开心", 35, 200.12, "女", 2);
insert into students values(0, "江配", 39, 196.12, "", 3);
insert into students values(0, "盛淑星", 26, 162.12, "女", 4);
insert into students values(0, "邓程飞", 19, 169.12, "男", 5);
insert into students values(0, "江铃", 18, 175.12, "女", 6);
insert into students values(0, "唐世菊", 13, 190.12, "男", 1);

select * from students;

-- 创建classes表(id、name)
create table classes(
　　id int unsigned not null auto_increment primary key,
　　name varchar(30)
　　gender enum("男", "女", "中性", "保密") default "保密"
);

insert into classes values(0, "python04大神");
select * from classes;

-- 查看表的创建语句
-- show create table 表名字;
show create table students;

-- 修改表-添加字段
-- alter table 表名 add 列名 类型;
alter table students add birthday datetime;

-- 修改表-修改字段：不重命名版
-- alter table 表名 modify 列名 类型及约束;
alter table students modify birthday date;

-- 修改表-修改字段：重命名版
-- alter table 表名 change 原名 新名 类型及约束;
alter table students change birthday birth date default "2000-01-01";

-- 修改表-删除字段
-- alter table 表名 drop 列名;
alter table students drop high;

-- 删除表
-- drop table 表名;
-- drop database 数据库;
-- drop table 数据表;
drop table xxxxx;

-- 增删改查(curd)

-- 增加
-- 全列插入
-- insert [into] 表名 values(...)
-- 主键字段 可以用 0 null default 来占位
-- 向classes表中插入 一个班级
insert into classes values(0, "菜鸟班");

+--------+-------------------------------------+------+-----+------------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------+-------------------------------------+------+-----+------------+----------------+
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| name | varchar(30) | YES | | NULL | |
| age | tinyint(3) unsigned | YES | | 0 | |
| gender | enum('男','女','中性','保密') | YES | | 保密 | |
| cls_id | int(10) unsigned | YES | | NULL | |
| birth | date | YES | | 2000-01-01 | |
+--------+-------------------------------------+------+-----+------------+----------------+

-- 向students表插入 一个学生信息
insert into students values(0, "小李飞刀", 20, "女", 1, "1990-01-01");
insert into students values(null, "小李飞刀", 20, "女", 1, "1990-01-01");
insert into students values(default, "小李飞刀", 20, "女", 1, "1990-01-01");

-- 失败
-- insert into students values(default, "小李飞刀", 20, "第4性别", 1, "1990-02-01");

-- 枚举中 的 下标从1 开始 1---“男” 2--->"女"....
insert into students values(default, "小李飞刀", 20, 1, 1, "1990-02-01");

-- 部分插入
-- insert into 表名(列1,...) values(值1,...)
insert into students (name, gender) values ("小乔", 2);

-- 多行插入
insert into students (name, gender) values ("大乔", 2),("貂蝉", 2);
insert into students values(default, "西施", 20, "女", 1, "1990-01-01"), (default, "王昭君", 20, "女", 1, "1990-01-01");

-- 修改
-- update 表名 set 列1=值1,列2=值2... where 条件;
update students set gender=1; -- 全部都改
update students set gender=1 where name="小李飞刀"; -- 只要name是小李飞刀的 全部的修改
update students set gender=1 where id=3; -- 只要id为3的 进行修改
update students set age=22, gender=1 where id=3; -- 只要id为3的 进行修改

-- 查询基本使用
-- 查询所有列
-- select * from 表名;
select * from students;

---定条件查询
select * from students where name="小李飞刀"; -- 查询 name为小李飞刀的所有信息
select * from students where id>3; -- 查询 name为小李飞刀的所有信息

-- 查询指定列
-- select 列1,列2,... from 表名;
select name,gender from students;

-- 可以使用as为列或表指定别名
-- select 字段[as 别名] , 字段[as 别名] from 数据表 where ....;
select name as 姓名,gender as 性别 from students;

-- 字段的顺序
select id as 序号, gender as 性别, name as 姓名 from students;

-- 删除
-- 物理删除
-- delete from 表名 where 条件
delete from students; -- 整个数据表中的所有数据全部删除
delete from students where name="小李飞刀";

-- 逻辑删除
-- 用一个字段来表示 这条信息是否已经不能再使用了
-- 给students表添加一个is_delete字段 bit 类型
alter table students add is_delete bit default 0;
update students set is_delete=1 where id=6;

-- 数据的准备

    -- 创建一个数据库

    create database python_test charset=utf8;

    -- 使用一个数据库

    use python_test;

    -- 显示使用的当前数据是哪个?

    select database();

    -- 创建一个数据表

    -- students表

    create table students(

        id int unsigned primary key auto_increment not null,

        name varchar(20), --default '',

        age tinyint unsigned default 0,

        height decimal(5,2),

        gender enum('男','女','中性','保密'),-- default '保密',

        cls_id int unsigned default 0,

        is_delete bit default 0

    );

    -- classes表

    create table classes (

        id int unsigned auto_increment primary key not null,

        name varchar(30) not null

    );

-- 查询

    -- 查询所有字段

    -- select * from 表名;

    select * from students;

    select * from classes;

    select id, name from classes;

    -- 查询指定字段

    -- select 列1,列2,... from 表名;

    select name, age from students;

    -- 使用 as 给字段起别名

    -- select 字段 as 名字.... from 表名;

    select name as 姓名, age as 年龄 from students;

    -- select 表名.字段 .... from 表名;

    select students.name, students.age from students;

    -- 可以通过 as 给表起别名

    -- select 别名.字段 .... from 表名 as 别名;

    select students.name, students.age from students;

    select s.name, s.age from students as s;

    -- 失败的select students.name, students.age from students as s;

    -- 消除重复行

    -- distinct 字段

    select distinct gender from students;

-- 条件查询

    -- 比较运算符

        -- select .... from 表名 where .....

        -- >

        -- 查询大于18岁的信息

        select * from students where age>18;

        select id,name,gender from students where age>18;

        -- <

        -- 查询小于18岁的信息

        select * from students where age<18;

        -- >=

        -- <=

        -- 查询小于或者等于18岁的信息

        -- =

        -- 查询年龄为18岁的所有学生的名字

        select * from students where age=18;

        -- != 或者 <>

    -- 逻辑运算符

        -- and

        -- 18到28之间的所以学生信息

        select * from students where age>18 and age<28;

        -- 失败select * from students where age>18 and <28;

        -- 18岁以上的女性

        select * from students where age>18 and gender="女";

        select * from students where age>18 and gender=2;

        -- or

        -- 18以上或者身高查过180(包含)以上

        select * from students where age>18 or height>=180;

        -- not

        - 不在 18岁以上的女性 这个范围内的信息

        -- select * from students where not age>18 and gender=2;

        select * from students where not (age>18 and gender=2);

        -- 年龄不是小于或者等于18 并且是女性

        select * from students where (not age<=18) and gender=2;

    -- 模糊查询

        -- like

        -- % 替换1个或者多个

        -- _ 替换1个

        -- 查询姓名中 以 "小" 开始的名字

        select name from students where name="小";

        select name from students where name like "小%";

        -- 查询姓名中 有 "小" 所有的名字

        select name from students where name like "%小%";

        -- 查询有2个字的名字

        select name from students where name like "__";

        -- 查询有3个字的名字

        select name from students where name like "__";

        -- 查询至少有2个字的名字

        select name from students where name like "__%";

        -- rlike 正则

        -- 查询以 周开始的姓名

        select name from students where name rlike "^周.*";

        -- 查询以 周开始、伦结尾的姓名

        select name from students where name rlike "^周.*伦$";

    -- 范围查询

        -- in (1, 3, 8)表示在一个非连续的范围内

        -- 查询 年龄为18、34的姓名

        select name,age from students where age=18 or age=34;

        select name,age from students where age=18 or age=34 or age=12;

        select name,age from students where age in (12, 18, 34);     

        -- not in 不非连续的范围之内

        -- 年龄不是 18、34岁之间的信息

        select name,age from students where age not in (12, 18, 34);

        -- between ... and ...表示在一个连续的范围内

        -- 查询 年龄在18到34之间的的信息

        select name, age from students where age between 18 and 34;

        -- not between ... and ...表示不在一个连续的范围内

        -- 查询 年龄不在在18到34之间的的信息

        select * from students where age not between 18 and 34;

        select * from students where not age between 18 and 34;

        -- 失败的select * from students where age not (between 18 and 34);

    -- 空判断

        -- 判空is null

        -- 查询身高为空的信息

        select * from students where height is null;

        select * from students where height is NULL;

        select * from students where height is Null;

        -- 判非空is not null

        select * from students where height is not null;

-- 排序

    -- order by 字段

    -- asc从小到大排列，即升序

    -- desc从大到小排序，即降序

    -- 查询年龄在18到34岁之间的男性，按照年龄从小到到排序

    select * from students where (age between 18 and 34) and gender=1;

    select * from students where (age between 18 and 34) and gender=1 order by age;

    select * from students where (age between 18 and 34) and gender=1 order by age asc;

    -- 查询年龄在18到34岁之间的女性，身高从高到矮排序

    select * from students where (age between 18 and 34) and gender=2 order by height desc; 

    -- order by 多个字段

    -- 查询年龄在18到34岁之间的女性，身高从高到矮排序, 如果身高相同的情况下按照年龄从小到大排序

;

    -- 查询年龄在18到34岁之间的女性，身高从高到矮排序, 如果身高相同的情况下按照年龄从小到大排序,

    -- 如果年龄也相同那么按照id从大到小排序

    select * from students where (age between 18 and 34) and gender=2 order by height desc,age asc,id desc;

    -- 按照年龄从小到大、身高从高到矮的排序

    select * from students order by age asc, height desc;

-- 聚合函数

    -- 总数

    -- count

    -- 查询男性有多少人，女性有多少人

    select * from students where gender=1;

    select count(*) from students where gender=1;

    select count(*) as 男性人数 from students where gender=1;

    select count(*) as 女性人数 from students where gender=2;

    -- 最大值

    -- max

    -- 查询最大的年龄

    select age from students;

    select max(age) from students;

    -- 查询女性的最高 身高

    select max(height) from students where gender=2;

    -- 最小值

    -- min

    -- 求和

    -- sum

    -- 计算所有人的年龄总和

    select sum(age) from students;

    -- 平均值

    -- avg

    -- 计算平均年龄

    select avg(age) from students;

    -- 计算平均年龄 sum(age)/count(*)

    select sum(age)/count(*) from students;

    -- 四舍五入 round(123.23 , 1) 保留1位小数

    -- 计算所有人的平均年龄，保留2位小数

    select round(sum(age)/count(*), 2) from students;

    select round(sum(age)/count(*), 3) from students;

    -- 计算男性的平均身高 保留2位小数

    select round(avg(height), 2) from students where gender=1;

    -- select name, round(avg(height), 2) from students where gender=1;

-- 分组

    -- group by

    -- 按照性别分组,查询所有的性别

    select name from students group by gender;

    --select * from students group by gender;

    select gender from students group by gender;

    -- 失败select * from students group by gender;

    -- 计算每种性别中的人数

    select gender,count(*) from students group by gender;

    -- 计算男性的人数

    select gender,count(*) from students where gender=1 group by gender;

    -- group_concat(...)

    -- 查询同种性别中的姓名

    select gender,group_concat(name) from students where gender=1 group by gender;

    select gender,group_concat(name, age, id) from students where gender=1 group by gender;

    select gender,group_concat(name, "_", age, " ", id) from students where gender=1 group by gender;

    -- having

    -- 查询平均年龄超过30岁的性别，以及姓名 having avg(age) > 30

    select gender, group_concat(name),avg(age) from students group by gender having avg(age)>30;    

    -- 查询每种性别中的人数多于2个的信息

    select gender, group_concat(name) from students group by gender having count(*)>2;

-- 分页

    -- limit start, count

    -- 限制查询出来的数据个数

    select * from students where gender=1 limit 2;

    -- 查询前5个数据

    select * from students limit 0, 5;

    -- 查询id6-10（包含）的书序

    select * from students limit 5, 5;

    -- 每页显示2个，第1个页面

    select * from students limit 0,2;

    -- 每页显示2个，第2个页面

    select * from students limit 2,2;

    -- 每页显示2个，第3个页面

    select * from students limit 4,2;

    -- 每页显示2个，第4个页面

    select * from students limit 6,2; -- -----> limit (第N页-1)*每个的个数, 每页的个数;

    -- 每页显示2个，显示第6页的信息, 按照年龄从小到大排序

    -- 失败select * from students limit 2*(6-1),2;

    -- 失败select * from students limit 10,2 order by age asc;

    select * from students order by age asc limit 10,2;

    select * from students where gender=2 order by height desc limit 0,2;

-- 连接查询

    -- inner join ... on

    -- select ... from 表A inner join 表B;

    select * from students inner join classes;

    -- 查询 有能够对应班级的学生以及班级信息

    select * from students inner join classes on students.cls_id=classes.id;

    -- 按照要求显示姓名、班级

    select students.*, classes.name from students inner join classes on students.cls_id=classes.id;

    select students.name, classes.name from students inner join classes on students.cls_id=classes.id;

    -- 给数据表起名字

    select s.name, c.name from students as s inner join classes as c on s.cls_id=c.id;

    -- 查询 有能够对应班级的学生以及班级信息，显示学生的所有信息，只显示班级名称

    select s.*, c.name from students as s inner join classes as c on s.cls_id=c.id;

    -- 在以上的查询中，将班级姓名显示在第1列

    select c.name, s.* from students as s inner join classes as c on s.cls_id=c.id;

    -- 查询 有能够对应班级的学生以及班级信息, 按照班级进行排序

    -- select c.xxx s.xxx from student as s inner join clssses as c on .... order by ....;

    select c.name, s.* from students as s inner join classes as c on s.cls_id=c.id order by c.name;

    -- 当时同一个班级的时候，按照学生的id进行从小到大排序

    select c.name, s.* from students as s inner join classes as c on s.cls_id=c.id order by c.name,s.id;

    -- left join

    -- 查询每位学生对应的班级信息

    select * from students as s left join classes as c on s.cls_id=c.id;

    -- 查询没有对应班级信息的学生

    -- select ... from xxx as s left join xxx as c on..... where .....

    -- select ... from xxx as s left join xxx as c on..... having .....

    select * from students as s left join classes as c on s.cls_id=c.id having c.id is null;

    select * from students as s left join classes as c on s.cls_id=c.id where c.id is null;

    -- right join   on

    -- 将数据表名字互换位置，用left join完成

-- 自关联

    -- 省级联动 url:http://demo.lanrenzhijia.com/2014/city0605/

    -- 查询所有省份

    select * from areas where pid is null;

    -- 查询出山东省有哪些市

    select * from areas as province inner join areas as city on city.pid=province.aid having province.atitle="山东省";

    select province.atitle, city.atitle from areas as province inner join areas as city on city.pid=province.aid having province.atitle="山东省";

    -- 查询出青岛市有哪些县城

    select province.atitle, city.atitle from areas as province inner join areas as city on city.pid=province.aid having province.atitle="青岛市";

    select * from areas where pid=(select aid from areas where atitle="青岛市";

-- 子查询

    -- 标量子查询

    -- 查询出高于平均身高的信息

    -- 查询最高的男生信息

    select * from students where height = 188;

    select * from students where height = (select max(height) from students);

    -- 列级子查询

    -- 查询学生的班级号能够对应的学生信息

    -- select * from students where cls_id in (select id from classes);