MySQL_入手<一>增--数据库操作

创建数据库

create database db_sanguo charset utf8;

切进db_sanguo

use db_sanguo

创建英雄

create table t_hero(
    id int unsigned auto_increment primary key,
    name varchar(10) unique not null,
    age tinyint unsigned default 0,
    gender set("男", "女"),
    state varchar(10)
);


insert into t_hero(name, age, gender, state) values("曹操","45","男","魏");
insert into t_hero(name, age, gender, state) values("刘备","43","男","蜀");
insert into t_hero(name, age, gender, state) values("孙权","42","男","吴");
insert into t_hero(name, age, gender, state) values("诸葛亮","36","男","蜀");
insert into t_hero(name, age, gender, state) values("司马懿","35","男","魏");
insert into t_hero(name, age, gender) values("貂蝉","22","女");
insert into t_hero(name, age, gender) values("吕布","30","男");
insert into t_hero(name, age, gender) values("小乔","20","女");
insert into t_hero(name, age, gender, state) values("关羽","35","男","蜀");
insert into t_hero(name, gender, state) values("孙尚香","女","吴");
insert into t_hero(name, age, gender, state) values("张飞","33","男","蜀");
insert into t_hero(name, gender, state) values("小张飞","男","吴");
insert into t_hero(name, age, gender, state) values("小张飞儿","33","男","蜀");
insert into t_hero(name, age, state) values("张小飞儿","33","蜀");

数据库的操作

查看所有存在的数据库
show databases;
使用数据库
use 数据库名;
查看当前选择的数据库
select database();
创建数据库
create database 数据库名 charset utf8;
例：
create database python charset utf8;
MySQL数据库默认编码是Latin1，如果在创建数据库忘记指定字符集为utf8，可以通过下面方法修改
show variables like "%char%";
+--------------------------+----------------------------+
| Variable_name            | Value                      |
+--------------------------+----------------------------+
| character_set_client     | utf8                       |
| character_set_connection | utf8                       |
| character_set_database   | latin1                     |
| character_set_filesystem | binary                     |
| character_set_results    | utf8                       |
| character_set_server     | latin1                     |
| character_set_system     | utf8                       |
| character_sets_dir       | /usr/share/mysql/charsets/ |
+--------------------------+----------------------------+

修改数据库 python_0314 的字符集
    alter database python charset utf8;
修改表的字符集，以及所有字符列(char, varchar, text等)的字符集为utf8
    alter table students convert to charset utf8;
删除数据库
drop database 数据库名;
例：
drop database python;
查看所有存在的数据库
show databases;
使用数据库
use 数据库名查看当前选择的数据库
select database();

删除数据库
drop database 数据库名;
例：
drop database python;

数据表的操作

查看当前数据库中所有表
show tables;
查看表结构
desc 表名;
创建表

auto_increment表示自动增长

create table 表名(列 类型 约束,...);

例：创建班级表

create table classes(
    id int unsigned auto_increment primary key not null,
    name varchar(10),
    isdelete bit default 0
);
例：创建学生表

create table students(
    id int unsigned auto_increment primary key not null,
    name varchar(10) not null,
    gender bit default 1,
    hometown varchar(20),
    clsid int unsigned,
    isdelete bit default 0,
    foreign key(clsid) references classes(id)
);

修改表-添加字段

alter table 表名 add 列名 类型;

alter table students add birthday datetime;
修改表-修改字段：重命名版

alter table 表名 change 原名 新名 类型及约束;

alter table students change name name1 varchar(20) not null;
修改表-修改字段：不重命名版

alter table 表名 modify 列名 类型及约束;

alter table students modify name1 varchar(10) not null;
修改表-删除字段

alter table 表名 drop 列名;

alter table students drop birthday;
删除表

drop table 表名;

drop table students;
查看表的创建语句

show create table 表名;

show create table students;

让数据表ID从零开始
方法1：
truncate table 你的表名
//这样不但将数据全部删除，而且重新定位自增的字段

方法2：
delete from 你的表名
dbcc checkident(你的表名,reseed,0) 
//重新定位自增的字段，让它从1开始

般mysql命令行中加;号代表一行命令的结束
c 可以退出当前行命令，
q或者exit退出mysql命令行