超全，建议收藏MySQL数据库常用sql命令语句集合

-- 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.p山东省";
        select province.atitle, city.atitle from areas as province inner join areas as city on city.p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.p青岛市";
        select * from areas where p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);