MySql基本语法（学习笔记)

select * from emp;  #注释

#---------------------------

#----命令行连接MySql---------

#启动mysql服务器

net start mysql

#关闭

net stop mysql

#进入

mysql -h 主机地址 -u 用户名 －p 用户密码

#退出

exit

#---------------------------

#----MySql用户管理---------

#修改密码:首先在DOS 下进入mysql安装路径的bin目录下，然后键入以下命令:

mysqladmin -uroot -p123 password 456;

#增加用户

#格式:grant 权限 on 数据库.* to 用户名@登录主机 identified by ‘密码‘

/*

如，增加一个用户user1密码为password1，让其可以在本机上登录， 并对所有数据库有查询、插入、修改、删除的权限。首先用以root用户连入mysql，然后键入以下命令：

grant select,insert,update,delete on *.* to [email protected] Identified by "password1";

如果希望该用户能够在任何机器上登陆mysql，则将localhost改为"%"。

如果你不想user1有密码，可以再打一个命令将密码去掉。

grant select,insert,update,delete on mydb.* to [email protected] identified by "";

*/

grant all privileges on wpj1105.* to [email protected] identified by ‘123‘;   #all privileges 所有权限

#----------------------------

#-----MySql数据库操作基础-----

#显示数据库

show databases;

#判断是否存在数据库wpj1105,有的话先删除

drop database if exists wpj1105;

#创建数据库

create database wpj1105;

#删除数据库

drop database wpj1105;

#使用该数据库

use wpj1105;

#显示数据库中的表

show tables;

#先判断表是否存在,存在先删除

drop table if exists student;

#创建表

create table student(

id int auto_increment primary key,

name varchar(50),

sex varchar(20),

date varchar(50),

content varchar(100)

)default charset=utf8;

#删除表

drop table student;

#查看表的结构

describe student;  #可以简写为desc student;

#插入数据

insert into student values(null,‘aa‘,‘男‘,‘1988-10-2‘,‘......‘);

insert into student values(null,‘bb‘,‘女‘,‘1889-03-6‘,‘......‘);

insert into student values(null,‘cc‘,‘男‘,‘1889-08-8‘,‘......‘);

insert into student values(null,‘dd‘,‘女‘,‘1889-12-8‘,‘......‘);

insert into student values(null,‘ee‘,‘女‘,‘1889-09-6‘,‘......‘);

insert into student values(null,‘ff‘,‘null‘,‘1889-09-6‘,‘......‘);

#查询表中的数据

select * from student;

select id,name from student;

#修改某一条数据

update student set sex=‘男‘ where id=4;

#删除数据

delete from student where id=5;

# and 且

select * from student where date>‘1988-1-2‘ and date<‘1988-12-1‘;

# or 或

select * from student where date<‘1988-11-2‘ or date>‘1988-12-1‘;

#between

select * from student where date between ‘1988-1-2‘ and ‘1988-12-1‘;

#in 查询制定集合内的数据

select * from student where id in (1,3,5);

#排序 asc 升序  desc 降序

select * from student order by id asc;

#分组查询 #聚合函数

select max(id),name,sex from student group by sex;

select min(date) from student;

select avg(id) as ‘求平均‘ from student;

select count(*) from student;   #统计表中总数

select count(sex) from student;   #统计表中性别总数  若有一条数据中sex为空的话,就不予以统计~

select sum(id) from student;

#查询第i条以后到第j条的数据(不包括第i条)

select * from student limit 2,5;  #显示3-5条数据

#巩固练习

create table c(

id int primary key auto_increment,

name varchar(10) not null,

sex varchar(50) ,  #DEFAULT ‘男‘ ,

age int unsigned, #不能为负值(如为负值 则默认为0)

sno int unique    #不可重复

);

drop table c;

desc c;

insert into c (id,name,sex,age,sno) values (null,‘涛哥‘,‘男‘,68,1);

insert into c (id,name,sex,age,sno) values (null,‘aa‘,‘男‘,68,2);

insert into c (id,name,sex,age,sno) values (null,‘平平‘,‘男‘,35,3);

...

select * from c;

#修改数据

update c set age=66 where id=2;

update c set name=‘花花‘,age=21,sex=‘女‘ where id=2

delete from c where age=21;

#常用查询语句

select name,age ,id from c

select * from c where age>40 and age<60;  #and

select * from c where age<40 or age<60;  #or

select * from c where age between 40 and 60 #between

select * from c where age in (30,48,68,99);     #in 查询指定集合内的数据

select * from c order by age desc;      #order by （asc升序 des降序）

#分组查询

select name,max(age) from c group by sex;  #按性别分组查年龄最大值

#聚合函数

select min(age) from c;

select avg(age) as ‘平均年龄 ‘ from c;

select count(*) from c;  #统计表中数据总数

select sum(age) from c;

#修改表的名字

#格式:alter table tbl_name rename to new_name

alter table c rename to a;

#表结构修改

create table test

(

id int not null auto_increment primary key, #设定主键

name varchar(20) not null default ‘NoName‘, #设定默认值

department_id int not null,

position_id int not null,

unique (department_id,position_id) #设定唯一值

);

#修改表的名字

#格式:alter table tbl_name rename to new_name

alter table test rename to test_rename;

#向表中增加一个字段(列)

#格式:alter table tablename add columnname type;/alter table tablename add(columnname type);

alter table test add  columnname varchar(20);

#修改表中某个字段的名字

alter table tablename change columnname newcolumnname type;  #修改一个表的字段名

alter table test change name uname varchar(50);

select * from test;

#表position 增加列test

alter table position add(test char(10));

#表position 修改列test

alter table position modify test char(20) not null;

#表position 修改列test 默认值

alter table position alter test set default ‘system‘;

#表position 去掉test 默认值

alter table position alter test drop default;

#表position 去掉列test

alter table position drop column test;

#表depart_pos 删除主键

alter table depart_pos drop primary key;

#表depart_pos 增加主键

alter table depart_pos add primary key PK_depart_pos

(department_id,position_id);

#用文本方式将数据装入数据库表中（例如D:/mysql.txt）

load data local infile "D:/mysql.txt" into table MYTABLE;

#导入.sql文件命令（例如D:/mysql.sql）