MYSQL数据库基本操作

//创建一个数据库
create database people;
//查看创建细节
show create database people;
//查看当前所有数据库
show databases;
//创建一个使用gbk字符集的数据库
create database people character set gbk;
//创建一个使用utf-8字符集并带校对规则的数据库
create database people character set utf8 collate utf8_general_ci;
//删除数据库
drop database people;

//创建表，首先选择数据库
mysql>use people;
mysql>create table stu(
id int,
name varchar(20),
gender varchar(20),
job varchar(20)
);
//向表中添加列（一般不采用，数据库应该是事先设定好）
mysql>alter table stu add image blob;
//删除表中的列
mysql>alter table stu drop image;
//修改job列的长度
mysql>alter table stu modify job varchar(60);
//修改表中列的名字
mysql>alter table stu change name username varchar(100);

//插入语句
mysql>insert into stu(id,name,gender,job) values(1,'张三','男','CTO');
//更新语句
mysql>update stu set name='李四' where id = 1;
mysql>update stu set salary = salary + 100 where name = '李四';
//删除数据
mysql>delete from stu;//删除全部数据
mysql>delete from stu where id = 1;//删除一条数据
//查询语句
mysql>select *from stu;//查询stu表中全部数据
mysql>select name from stu;//查询表中所有的名字
mysql>selsect name 姓名 from stu;//查询表中所有名字并将列输出为名字而不是name;
mysql>select *from stu where id = 1;//查询id为1的所有数据
mysql>select *from stu where id>3;//查询id大于3的所有数据
mysql>select *from stu where id between 5 and 10;//查询id在5-10中的数据
mysql>select *from stu where id in(1,5,7);//查询id为1，5，7的数据

//模糊查询
mysql>select *from stu where name = '李%'//查询所有姓李的数据
mysql>select *from stu where name = '%李%'//查询名字中含有李的数据
mysql>selsect *from stu where name = '_李%'//查询姓名中第二个字为李的数据
//排序查询
mysql>select *from stu order by math desc;//对数学成绩降序查询
mysql>select *from stu order by math asc;//对数学成绩升序查询

//交叉查询stu中三条数据worker中四条数据，查询结果3*4=12条数据
mysql>select *from stu cross join worker;
//外链接
left out join = left join;
mysql>select *from customer c left join orders o on c.id=o.customer_id;//查询前表中id和后表中customer_id相同的数据

mysql>select *from orders where customer_id=(select id from customer where name = '张三');

mysql>select *from orders where age>20 union selsect orders where customer_id = 1;

//统计班级人数
mysql>select count(*) from stu;
//统计数学成绩大于90的学生个数
mysql>select count(*) from stu where math>90;
//统计表中数学成绩的总和
mysql>select sum(math) from stu;
//统计表中数学,语文，英语成绩的总和
mysql>select sum(math),sum(chinese),sum(english) from stu;
//统计语文平均分
mysql>select avg(chinese) from stu;
//统计语文最高分和最低分
mysql>select max(chinese),min(chinese) from stu;