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exitstatus;显示当前mysql的version的各种信息。 #---------------------------#----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 user1@localhost 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 user1@localhost identified by "";*/ grant all privileges on wpj1105.* to sunxiao@localhost 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';  #betweenselect * 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=2delete from c where age=21; #常用查询语句select name,age ,id from cselect * from c where age>40 and age<60;  #andselect * from c where age<40 or age<60;  #orselect * from c where age between 40 and 60 #betweenselect * 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_namealter 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_namealter 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testalter table position add(test char(10));#表position 修改列testalter 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testalter 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）source d:/mysql.sql;  #或者  /. d:/mysql.sql;