-- 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    -- 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);    select * from students;    -- 创建classes表(id、name)    create table classes(        id int unsigned not null auto_increment primary key,        name varchar(30)    );    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	select * from students where (age between 18 and 34) and gender=2 order by height desc,id desc;	-- 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);