创建表：
create table customer(mid char(5) primary key,name varchar(20),birth date,sex char(1) DEFAULT '0');
显示表的结构;
desc customer;
插入：
insert customer values('N001','小小','1980-12-12',1);
检索;
select* from customer;
创建表的时候指定字符集:
create table customer(mid char(5) primary key,name varchar(20),birth date,sex char(1) DEFAULT '0')
charset=utf8;
显示所有的表;
show tables;
显示表的结构 desc customer;
删除表:drop table customer;
自增序列 auto_increment
create table goods(id int auto_increment primary key,name varchar(30));
insert into goods(name) value('桃子');
insert into customer(mid,name,sex)values('H0001','李佳',0);
insert into customer(mid,name,birth) values('G0001','杜依依','1974-09-18');
insert into customer(mid,name,sex)values('G0001','李玉',0);
更新存在的记录：
update customer set name='李玉枝',birth='1997-12-24' where mid='N001';
update customer set sex='0';
删除表中的记录;
delete from customer where mid='N002';
清除所有的数据;
truncate table customer;
数据检索select;
1.推荐明确指定列名
select mid,name from customer;
2.条件检索
select name,birth from customer where birth>='1980/01/01';
3.模糊检索
select name,birth from customer where name like '李%';
select name,birth from customer where name like '李_';
4.null条件
select name,birth from customer where birth is NUll;
5.多个组合表达
select name,birth from customer where sex='0' and birth is not null;
select name,birth from customer where sex='0' or birth<'2000/3/3';
运算符优先级：not <and<or
6.结果排序; asc升序 desc 降序
select name,birth from customer order by sex asc,birth desc;
7.去得指定件数的记录 （eg：第5名到第九名的数据）
select name,birth from customer order by birth desc limit 2;
原则上limit语句要和order by语句同时使用，没同时使用则取出随机结果
8.数据分组
以特定字对记录进行整理称为分组化，group by 通常与统计函数进行使用
avg 平均数
count 件数
max 最大值
min 最小值
sum 合计值
统计男生女生多少人：
select sex ,count(mid) from customer group by sex;
9.列的别名
select sex ,count(mid) as cnt from customer group by sex;
count 统计的是非null的记录