MYSQL 数据库简介
MYSQL 数据库操作命令
1. 数据库增删改查命令
登录数据库命令：
mysql -u root -p，退出：quit;
查询数据库：show databases;
创建数据库：create databasename;
删除数据库：drop databasename;
使用数据库：use databasename；
2. 表的增删改查
查看表：
show tables;
删除表：drop tables user
创建表：create table user(id int, username varchr(40), password varcha(32));
查看键、表的语句：show create table username
查看表结构：desc tablename;
修改表字段的值：alter table user modify name varchar(30);
修改表字段名：alter table user change password pass varchar(45);
删除表的字段：alter table user drop password;
添加字段：alter table user add pass varchar(32) after name;
修改表名：alter table user rename user_table;
为字段添加普通索引：alter table user add index(name)；
为字段添加唯一索引：alter table user add unique(password);
添加全文索引：alter table user add fulltext(address);
添加主键索引：alter table user add primiry key(id);
查看都有哪些字段加索引：show index from user;
查看表在那个数据库中：select database();
在表中插入数据：insert into user values(1,'spring','123123','China');常用：insert into user (name,password,address) values('tom','123123','china');
同时插入多条数据：insert into user (name,password,address) values('joe','123','henan'),('Jely','45','Amarica');
查询是否插入成功：select * from user;
删除字段：delete from user where name='Jely';
修改字段：update user set name='Summer',password='123123' where id=2;
查询字段：select name from user;
去除查询字段重复值：select distinct address from user;
3. select 查询语句
between取区间值查询:
select * from user where id between 2 and 5;
in 查询：select * from user where age in(15,16,17);
取反查询：select * from user where age !=50;
like模糊查询：select * from user where address like '%h%';
升序排列：select * from user order by age asc(可默认不写);
降序排列：select * from user order by age desc;
查询几条：select * from user limit 3,4;
分组：select * from user group by address;
查询数据总数：select count(*) from user;
起别名：select username as name from user;
内链查询：select username . gname from shop_user inner join shop_goods on shop_user.gid = shop_goods.gid;
左链查询：select shop_user.username from shop_user left join shop_goods on shop_user.gid = shop_goods.gid;
右链查询：select shop_user.username from shop_user right join shop_goods on shop_user.gid = shop_goods.gid;
嵌套查询：select * from shop_user where gid in(select gid from shop_goods);
