mysql基本功能

SQL structed query language

连接MYSQL服务器：mysql -uroot -proot

数据库的操作：创建，查看，修改，删除
 *创建：
  创建一个名称为mydb1的数据库。
   create database mydb1;
  创建一个使用utf-8字符集的mydb2数据库。
   create database mydb2 character set utf8;
  创建一个使用utf-8字符集，并带校对规则的mydb3数据库。
   create database mydb2 character set utf8 collate utf8_general_ci;
 *查看:
  显示所有数据库
   show databases;
  显示创建数据库的语句信息
   show create database mydb2;
 *修改:
  修改mydb1的字符集为gbk(不能修改数据库名)
   alter database mydb1 character set utf8; 
 *删除:
  删除数据库mydb2
   drop database mydb1;

表的操作：创建，查看，修改，删除
 *创建：
  根据实体类Person创建表person
   Person {
    int id;
    String name;
   }
   create table person(
    id int,
    name varchar(20)
   );
  mysql中的数据类型：
   bit 1位　但可以指定位数，如：bit<3>
   int 2字节 可以指定最大位数，如：int<4>　最大为4位的整数
   float 2个字节　可以指定最大的位数和最大的小数位数，如：float<5,2> 最大为一个５位的数，小数位最多2位
   double　4个字节　可以指定最大的位数和最大的小数位数，如：float<6,4> 最大为一个6位的数，小数位最多4位
   char　必须指定字符数,如char(5) 为不可变字符　即使存储的内容为'ab',也是用5个字符的空间存储这个数据
   varchar　必须指定字符数,如varchar(5) 为可变字符　如果存储的内容为'ab',占用2个字符的空间；如果为'abc',则占用3个字符的空间
   text: 大文本(大字符串)
   blob：二进制大数据　如图片，音频文件，视频文件
   date: 日期　如：'1921-01-02'
   datetime: 日期时间　如：'1921-01-02 12:23:43'
   timeStamp: 时间戳，自动赋值为当前日期时间
   
  创建一个员工表
   create table employee(
    id int,
    name varchar(20),
    sex bit,
    birthday date,
    entry_date date,
    job varchar(20),
    salary double,
    resume text
   );
 *查看：
  查看所有的表：
   show tables;
  查看指定表的创建语句
   show create table employee;
  显示指定表的结构：
   desc employee;
 *删除：
  删除employee表
  drop table employee;
 *修改表：
  增加一个字段：alter table worker add column height double;
  修改一个字段：alter table worker modify column height float;
  删除一个字段：alter table worker drop column height;
  更改表名：rename table employee to worker;
  修改表的字符集:alter table worker character set gbk;
 
表数据的CRUD
 *C(create增加数据) Insert语句
  新建Employee表并表中添加一些记录
   create table employee(
    id int,
    name varchar(20),
    sex bit,
    birthday date,
    salary double,
    entry_date date,
    resume text
   );
   insert into employee(name,id,sex,birthday,salary,entry_date,resume) values('张三',1,1,'1983-09-21',15000,'2012-06-24','一个大牛');
   insert into employee(id,name,sex,birthday,salary,entry_date,resume) values(2,'李四',1,'1984-09-21',10000,'2012-07-24','一个中牛');
   insert into employee(id,name,sex,birthday,salary,entry_date,resume) values(3,'王五',0,'1985-09-21',7000,'2012-08-24','一个小牛');
 
 *U(update更新数据) Update语句
  将所有员工薪水都增加500元。
   update employee set salary=salary+500;
  将王五的员工薪水修改为10000元，resume改为也是一个中牛
   update employee set salary=10000,resume='也是一个中牛' where name='王五';
 *D(drop删除数据) Delete语句
  删除表中姓名为王五的记录。
   delete from employee where name='王五';
  删除表中所有记录。
   delete from employee; --可以有条件，但删除所有记录差了一点
  使用truncate删除表中记录。
   truncate employee;--无条件 效率高
 
 *R(Retrieve查找数据) Select语句 
  准备环境：
   create table student(
    id int,
    name varchar(20),
    chinese int,
    english int,
    math int
   );

   insert into student(id,name,chinese,english,math) values(1,'何东',80,85,90);
   insert into student(id,name,chinese,english,math) values(2,'权筝',90,95,95);
   insert into student(id,name,chinese,english,math) values(3,'何南',80,96,96);
   insert into student(id,name,chinese,english,math) values(4,'叶坦',81,97,85);
   insert into student(id,name,chinese,english,math) values(5,'何西',85,84,90);
   insert into student(id,name,chinese,english,math) values(6,'丁香',92,85,87);
   insert into student(id,name,chinese,english,math) values(7,'何北',75,81,80);
   insert into student(id,name,chinese,english,math) values(8,'唐娇',77,80,79);
   insert into student(id,name,chinese,english,math) values(9,'任知了',95,85,85);
   insert into student(id,name,chinese,english,math) values(10,'王越',94,85,84);

  查询表中所有学生的信息。
   select * from student;
  查询表中所有学生的姓名和对应的英语成绩。
   select name,english from student;
  过滤表中重复数据。
   select english from student;
   select DISTINCT english from student;
   select DISTINCT english,name from student;

   select english+chinese+math from student;
   select english+chinese+math as 总分 from student;
   select name,english+chinese+math as 总分 from student;

  在所有学生英语分数上加10分特长分。
   select name,english+10 from student;
  统计每个学生的总分。
   select english+chinese+math from student;
  使用别名表示学生分数
   select name,english+chinese+math as 总分 from student;
   select name,english+chinese+math 总分 from student;

  查询姓名为何东的学生成绩
   select * from student where name='何东';
  查询英语成绩大于90分的同学
   select * from student where english>90;
  查询总分大于250分的所有同学
   select * from student where english+chinese+math>250;

  查询英语分数在 85－95之间的同学。
   select * from student where english>=85 and english<=95;
   select * from student where english between 85 and 95;
  查询数学分数为84,90,91的同学。
   select * from student where math=84 or math=90 or math=91;
   select * from student where math in(84,90,91);
  查询所有姓何的学生成绩。
   select * from student where name like '何%';
  查询数学分>85，语文分>90的同学。
   select * from student where math>85 and chinese>90;

  对数学成绩排序后输出。
   select * from student order by math;
  对总分排序后输出，然后再按从高到低的顺序输出
   select * from student order by math+chinese+english desc;
  对姓何的学生成绩排序输出
   select * from student where name like '何%' order by math+chinese+english desc;
   select name, math+chinese+english from student where name like '何%' order by math+chinese+english desc;

  统计一个班级共有多少学生？
   select count(*) from student;
  统计数学成绩大于90的学生有多少个？
   select count(*) from student where math>90;
  统计总分大于250的人数有多少？
   select count(*) from student where math+chinese+english>250;

  统计一个班级数学总成绩？
   select sum(math) from student;
  统计一个班级语文、英语、数学各科的总成绩
   select sum(math), sum(chinese), sum(english) from student;
  统计一个班级语文、英语、数学的成绩总和
   select sum(math+chinese+english)from student;
   select sum(math)+sum(chinese)+sum(english) from student;

  求一个班级数学平均分？
   select avg(math) from student;
  求一个班级总分平均分
   select avg(math+chinese+english)from student;
   select avg(math)+avg(chinese)+avg(english) from student;

  求班级最高分和最低分
   select max(math+chinese+english),min(math+chinese+english) from student;
 
  查出各个班的总分，最高分
   准备环境
    给表添加一个字段：alter table student add column class_id int;
    更新表：
     update student set class_id=1 where id<=5;
     update student set class_id=2 where id>5;
   select sum(math+chinese+english),max(math+chinese+english) from student group by class_id;

  查询出班级总分大于1300分的班级ID
   select class_id from student group by class_id having sum(math+chinese+english)>1300;

表的约束　　
 *定义主键约束　primary key:不允许为空，不允许重复

 *定义主键自动增长　auto_increment

 *定义唯一约束　unique

 *定义非空约束　not null

 *定义外键约束　constraint ordersid_FK foreign key(ordersid) references orders(id)

 *删除主键：alter table tablename drop primary key ;
 
数据的备份与恢复：
 *准备数据：
  create database mydb1;
  use mydb1;
  create table user(
   id int,
   name varchar(20)
  );
  insert into user(id,name) values(1,'Tom');
  select * from user;
 *备份：
  mysqldump -uroot -p mydb1>d:\test.sql;--备份数据库里的数据

 *恢复；
  mysql -uroot -p mydb1
  source d:\test.sql(在mysql客户端上执行)
 
多表查询与子查询：
 准备环境：
  部门表
   CREATE TABLE DEPARTMENT(
      department_id int primary key auto_increment,      
      name varchar
   );
  职位表
   CREATE TABLE LOCATION (
      location_id int PRIMARY KEY auto_increment,      
      name varchar
   );
  员工表
   CREATE TABLE EMPLOYEES(
      employee_id int PRIMARY KEY auto_increment,      
      department_id int,      
      location_id int,      
      first_name varchar,      
      last_name varchar,      
      salary double,
      hire_date date    
   );

  向department表中添加数据   
   insert into department(name) values ('人事');
   insert into department(name) values ('财务');
   insert into department(name) values ('后勤');
   insert into department(name) values ('公关');
   insert into department(name) values ('研发');
  
  向location表中添加数据
   insert into location(name) values ('总经理');
   insert into location(name) values ('经理');
   insert into location(name) values ('主管');
   insert into location(name) values ('组长');
   insert into location(name) values ('职员');
  向employees表中添加数据
   insert into employees(department_id,location_id , first_name, last_name, salary,hire_date)
       values (1,1, 'A', 'z', 50000, '2005-02-21');      
   insert into employees(department_id,location_id, first_name, last_name, salary,hire_date)
       values (1,2, 'B', 'x', 20000, '2009-03-21');      
   insert into employees(department_id,location_id , first_name, last_name, salary,hire_date)
       values (2,3, 'C', 'v', 10000, '2009-08-23');      
   insert into employees(department_id,location_id, first_name, last_name, salary,hire_date)
       values (4,2, 'D', 'n', 30000, '2004-09-28');      
   insert into employees(department_id,location_id, first_name, last_name, salary,hire_date)
       values (3,5, 'E', 'm', 3000, '2009-04-11');      
   insert into employees(department_id,location_id, first_name, last_name, salary,hire_date)
       values (5,5, 'F', 'l', 5000, '2008-03-11');      
   insert into employees(department_id,location_id, first_name, last_name, salary,hire_date)
       values (5,3, 'G', 'p', 20000, '2005-05-09');      
   insert into employees(department_id,location_id, first_name, last_name, salary,hire_date)
       values (5,4, 'H', 'o', 8000, '2006-07-21');      
   insert into employees(department_id,location_id, first_name, last_name, salary,hire_date)
       values (5,5, 'I', 'u', 6000, '2006-09-21');      
   insert into employees(department_id,location_id, first_name, last_name, salary,hire_date)
       values (5,5, 'J', 'y', 5500, '2007-08-21');      
   insert into employees(department_id,location_id, first_name, last_name, salary,hire_date)
       values (5,5, 'K', 't', 6500, '2006-12-21');      
   insert into employees(department_id,location_id, first_name, last_name, salary,hire_date)
       values (5,1, 'L', 'r', 100000, '2001-05-21');
 练习： 
 --多表查询：查出姓z的员工的所有信息
  select * from employees e, department d, location l
   where e.[department_id]=d.[department_id] and e.[location_id]=l.[location_id] and e.[last_name]='z';
 --单行子查询: 查出所有工资大于平均工资的员工信息
  select * from employees where salary >(select avg(salary) from employees)
 --多行子查询: 查出所有所有姓z的部门名称
  select name from department where department_id in (select department_id from employees where last_name='z');