SQL种类：
DDL:数据定义语言
DML：数据操作语言
DQL：数据查询语言
DCL：数据控制语言
DDL:
- show databases; //查询数据库
- create database if not exists sqldb;//创建一个数据库
- use sqldb; //使用一个sqldb
- show tables; //显示表
- create table if not exists cats(id int not null auto_increment, pid int not null default '0', name varchar(16) not null default '', desn text not null default '', primay key(id), key name(name, pid)); //创建数据表
- create table if not null exists products(id int not null auto_increment, cid int not null default '0', name varchar(16) not null default '', num int not null default '0', price double(10, 2) not null default '0.00', desn text not null default '', primary key(id), key name(name, price));//创建表
DML:数据操作语言 insert update delete
- desc products; //查看表结构
- insert into products(cid, name, price, num, desn) values('0', 'dda', '10.20', '2', 'this is a java');// 插入记录
- insert into products values(null, '0', 'java', '10', '10.10', 'this is a java!');
- update procudts set num = 1 where id = 1;//更新语句
- update products set name = 'php', desn = 'this is php' where id = 2; //更新语句
- delete from products where id = 1;//删除id = 1的记录
DQL:数据查询语句
select [all | distinct]
[字段名 as 别名]
from
表名
[where 条件语句]
[group by ....]
[having....]
[order by...]
[limit count]
- where 语句 select update delete
逻辑运算（多个条件）
&& || !
and or not
比较运算
<=>
>
<
=
!= / <>
>=
<=
IS NULL
NOT NULL
BETWEEN AND
NOT BETWEEN AND
IN
LIKE 模糊查询 _：一个任意字符 %：0个或者多个字符
NOT LIKE：
REGEXP 正则表达式