一篇就夠了——數據庫的基本操作

-- 鏈接數據庫
mysql -uroot -p
mysql -uroot -pmysql

-- 退出數據庫
exit/quit/ctrl+d


-- sql語句最後需要有分號;結尾
-- 顯示數據庫版本
select version();

-- 顯示時間
select now();

-- 查看所有數據庫
show databases;


-- 創建數據庫
-- create database 數據庫名 charset=utf8;
create database python04;
create database python04new charset=utf8;


-- 查看創建數據庫的語句
-- show crate database ....
show create database python04;


-- 查看當前使用的數據庫
select database();

-- 使用數據庫
-- use 數據庫的名字
use python04new;

-- 刪除數據庫
-- drop database 數據庫名;
drop database python04;

– 數據表的操作

-- 查看當前數據庫中所有表
show tables;


-- 創建表
-- auto_increment表示自動增長
-- not null 表示不能爲空
-- primary key 表示主鍵
-- default 默認值
-- create table 數據表名字 (字段 類型 約束[, 字段 類型 約束]);
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)
);

-- 查看錶結構
-- desc 數據表的名字;
desc xxxxx;

-- 創建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;

-- 創建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;

-- 查看錶的創建語句
-- show create table 表名字;
show create table students;


-- 修改表-添加字段
-- alter table 表名 add 列名 類型;
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 類型及約束;
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 類型及約束;
alter table students change birthday birth date default "2000-01-01";


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


-- 刪除表
-- drop table 表名;
-- drop database 數據庫;
-- drop table 數據表;
drop table xxxxx;

– 增刪改查(curd)

-- 增加
    -- 全列插入
    -- insert [into] 表名 values(...)
    -- 主鍵字段 可以用 0  null   default 來佔位
    -- 向classes表中插入 一個班級
    insert into classes values(0, "菜鳥班");


    +--------+-------------------------------------+------+-----+------------+----------------+
    | 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 一個學生信息
    insert into students values(0, "小李飛刀", 20, "女", 1, "1990-01-01");
    insert into students values(null, "小李飛刀", 20, "女", 1, "1990-01-01");
    insert into students values(default, "小李飛刀", 20, "女", 1, "1990-01-01");

    -- 失敗
    -- insert into students values(default, "小李飛刀", 20, "第4性別", 1, "1990-02-01");

    -- 枚舉中 的 下標從1 開始 1---“男” 2--->"女"....
    insert into students values(default, "小李飛刀", 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 ("小喬", 2);


    -- 多行插入
    insert into students (name, gender) values ("大喬", 2),("貂蟬", 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 條件;
    update students set gender=1; -- 全部都改
    update students set gender=1 where name="小李飛刀"; -- 只要name是小李飛刀的 全部的修改
    update students set gender=1 where id=3; -- 只要id爲3的 進行修改
    update students set age=22, gender=1 where id=3; -- 只要id爲3的 進行修改

-- 查詢基本使用
    -- 查詢所有列
    -- select * from 表名;
    select * from students;

    ---定條件查詢
    select * from students where name="小李飛刀"; -- 查詢 name爲小李飛刀的所有信息
    select * from students where id>3; -- 查詢 name爲小李飛刀的所有信息


    -- 查詢指定列
    -- select 列1,列2,... from 表名;
    select name,gender from students;


    -- 可以使用as爲列或表指定別名
    -- select 字段[as 別名] , 字段[as 別名] from 數據表 where ....;
    select name as 姓名,gender as 性別 from students;


    -- 字段的順序
    select id as 序號, gender as 性別, name as 姓名 from students;


-- 刪除
    -- 物理刪除
    -- delete from 表名 where 條件
    delete from students; -- 整個數據表中的所有數據全部刪除
    delete from students where name="小李飛刀";

    -- 邏輯刪除
    -- 用一個字段來表示 這條信息是否已經不能再使用了
    -- 給students表添加一個is_delete字段 bit 類型
    alter table students add is_delete bit default 0;
    update students set is_delete=1 where id=6;

– 數據的準備
– 創建一個數據庫
create database python_test charset=utf8;

-- 使用一個數據庫
use python_test;

-- 顯示使用的當前數據是哪個?
select database();

-- 創建一個數據表
-- 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
);

– 查詢
– 查詢所有字段
– select * from 表名;
select * from students;
select * from classes;
select id, name from classes;

-- 查詢指定字段
-- select 列1,列2,... from 表名;
select name, age from students;

-- 使用 as 給字段起別名
-- select 字段 as 名字.... from 表名;
select name as 姓名, age as 年齡 from students;

-- select 表名.字段 .... from 表名;
select students.name, students.age from students;


-- 可以通過 as 給表起別名
-- select 別名.字段 .... from 表名 as 別名;
select students.name, students.age from students;
select s.name, s.age from students as s;
-- 失敗的select students.name, students.age from students as s;


-- 消除重複行
-- distinct 字段
select distinct gender from students;

– 條件查詢
– 比較運算符
– select … from 表名 where …
– >
– 查詢大於18歲的信息
select * from students where age>18;
select id,name,gender from students where age>18;

	-- <
	-- 查詢小於18歲的信息
	select * from students where age<18;

	-- >=
	-- <=
	-- 查詢小於或者等於18歲的信息

	-- =
	-- 查詢年齡爲18歲的所有學生的名字
	select * from students where age=18;


	-- != 或者 <>


-- 邏輯運算符
	-- and
	-- 18到28之間的所以學生信息
	select * from students where age>18 and age<28;
	-- 失敗select * from students where age>18 and <28;


	-- 18歲以上的女性
	select * from students where age>18 and gender="女";
	select * from students where age>18 and gender=2;


	-- or
	-- 18以上或者身高查過180(包含)以上
	select * from students where age>18 or height>=180;


	-- not
	-- 不在 18歲以上的女性 這個範圍內的信息
	-- select * from students where not age>18 and gender=2;
	select * from students where not (age>18 and gender=2);

	-- 年齡不是小於或者等於18 並且是女性
	select * from students where (not age<=18) and gender=2;


-- 模糊查詢
	-- like 
	-- % 替換1個或者多個
	-- _ 替換1個
	-- 查詢姓名中 以 "小" 開始的名字
	select name from students where name="小";
	select name from students where name like "小%";

	-- 查詢姓名中 有 "小" 所有的名字
	select name from students where name like "%小%";

	-- 查詢有2個字的名字
	select name from students where name like "__";

	-- 查詢有3個字的名字
	select name from students where name like "__";

	-- 查詢至少有2個字的名字
	select name from students where name like "__%";


	-- rlike 正則
	-- 查詢以 周開始的姓名
	select name from students where name rlike "^周.*";

	-- 查詢以 周開始、倫結尾的姓名
	select name from students where name rlike "^周.*倫$";


-- 範圍查詢
	-- in (1, 3, 8)表示在一個非連續的範圍內
	-- 查詢 年齡爲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 不非連續的範圍之內
	-- 年齡不是 18、34歲之間的信息
	select name,age from students where age not in (12, 18, 34);


	-- between ... and ...表示在一個連續的範圍內
	-- 查詢 年齡在18到34之間的的信息
	select name, age from students where age between 18 and 34;

	
	-- not between ... and ...表示不在一個連續的範圍內
	-- 查詢 年齡不在在18到34之間的的信息
	select * from students where age not between 18 and 34;
	select * from students where not age between 18 and 34;
	-- 失敗的select * from students where age not (between 18 and 34);


-- 空判斷
	-- 判空is null
	-- 查詢身高爲空的信息
	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從小到大排列，即升序
– desc從大到小排序，即降序

-- 查詢年齡在18到34歲之間的男性，按照年齡從小到到排序
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;


-- 查詢年齡在18到34歲之間的女性，身高從高到矮排序
select * from students where (age between 18 and 34) and gender=2 order by height desc;


-- order by 多個字段
-- 查詢年齡在18到34歲之間的女性，身高從高到矮排序, 如果身高相同的情況下按照年齡從小到大排序
select * from students where (age between 18 and 34) and gender=2 order by height desc,id desc;


-- 查詢年齡在18到34歲之間的女性，身高從高到矮排序, 如果身高相同的情況下按照年齡從小到大排序,
-- 如果年齡也相同那麼按照id從大到小排序
select * from students where (age between 18 and 34) and gender=2 order by height desc,age asc,id desc;


-- 按照年齡從小到大、身高從高到矮的排序
select * from students order by age asc, height desc;

– 聚合函數
– 總數
– count
– 查詢男性有多少人，女性有多少人
select * from students where gender=1;
select count() from students where gender=1;
select count() as 男性人數 from students where gender=1;
select count(*) as 女性人數 from students where gender=2;

-- 最大值
-- max
-- 查詢最大的年齡
select age from students;
select max(age) from students;

-- 查詢女性的最高 身高
select max(height) from students where gender=2;

-- 最小值
-- min


-- 求和
-- sum
-- 計算所有人的年齡總和
select sum(age) from students;


-- 平均值
-- avg
-- 計算平均年齡
select avg(age) from students;


-- 計算平均年齡 sum(age)/count(*)
select sum(age)/count(*) from students;


-- 四捨五入 round(123.23 , 1) 保留1位小數
-- 計算所有人的平均年齡，保留2位小數
select round(sum(age)/count(*), 2) from students;
select round(sum(age)/count(*), 3) from students;

-- 計算男性的平均身高 保留2位小數
select round(avg(height), 2) from students where gender=1;
-- select name, round(avg(height), 2) from students where gender=1;

– 分組

-- group by
-- 按照性別分組,查詢所有的性別
select name from students group by gender;
select * from students group by gender;
select gender from students group by gender;
-- 失敗select * from students group by gender;

-- 計算每種性別中的人數
select gender,count(*) from students group by gender;


-- 計算男性的人數
select gender,count(*) from students where gender=1 group by gender;


-- group_concat(...)
-- 查詢同種性別中的姓名
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
-- 查詢平均年齡超過30歲的性別，以及姓名 having avg(age) > 30
select gender, group_concat(name),avg(age) from students group by gender having avg(age)>30;

-- 查詢每種性別中的人數多於2個的信息
select gender, group_concat(name) from students group by gender having count(*)>2;

– 分頁
– limit start, count

-- 限制查詢出來的數據個數
select * from students where gender=1 limit 2;

-- 查詢前5個數據
select * from students limit 0, 5;

-- 查詢id6-10（包含）的書序
select * from students limit 5, 5;


-- 每頁顯示2個，第1個頁面
select * from students limit 0,2;

-- 每頁顯示2個，第2個頁面
select * from students limit 2,2;

-- 每頁顯示2個，第3個頁面
select * from students limit 4,2;

-- 每頁顯示2個，第4個頁面
select * from students limit 6,2; -- -----> limit (第N頁-1)*每個的個數, 每頁的個數;

-- 每頁顯示2個，顯示第6頁的信息, 按照年齡從小到大排序
-- 失敗select * from students limit 2*(6-1),2;
-- 失敗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;

– 連接查詢
– inner join … on

-- select ... from 表A inner join 表B;
select * from students inner join classes;

-- 查詢 有能夠對應班級的學生以及班級信息
select * from students inner join classes on students.cls_id=classes.id;

-- 按照要求顯示姓名、班級
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;

-- 給數據表起名字
select s.name, c.name from students as s inner join classes as c on s.cls_id=c.id;

-- 查詢 有能夠對應班級的學生以及班級信息，顯示學生的所有信息，只顯示班級名稱
select s.*, c.name from students as s inner join classes as c on s.cls_id=c.id;

-- 在以上的查詢中，將班級姓名顯示在第1列
select c.name, s.* from students as s inner join classes as c on s.cls_id=c.id;

-- 查詢 有能夠對應班級的學生以及班級信息, 按照班級進行排序
-- 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;

-- 當時同一個班級的時候，按照學生的id進行從小到大排序
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
-- 查詢每位學生對應的班級信息
select * from students as s left join classes as c on s.cls_id=c.id;

-- 查詢沒有對應班級信息的學生
-- 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
-- 將數據表名字互換位置，用left join完成

– 自關聯
– 省級聯動 url:http://demo.lanrenzhijia.com/2014/city0605/

-- 查詢所有省份
select * from areas where pid is null;

-- 查詢出山東省有哪些市
select * from areas as province inner join areas as city on city.pid=province.aid having province.atitle="山東省";
select province.atitle, city.atitle from areas as province inner join areas as city on city.pid=province.aid having province.atitle="山東省";

-- 查詢出青島市有哪些縣城
select province.atitle, city.atitle from areas as province inner join areas as city on city.pid=province.aid having province.atitle="青島市";
select * from areas where pid=(select aid from areas where atitle="青島市")

– 子查詢
– 標量子查詢
– 查詢出高於平均身高的信息

-- 查詢最高的男生信息
select * from students where height = 188;
select * from students where height = (select max(height) from students);

-- 列級子查詢
-- 查詢學生的班級號能夠對應的學生信息
-- select * from students where cls_id in (select id from classes);