迟到的整理笔记，记录小编自己所知所学。互联网是有记忆的
ANSI，美国国家标准化组织
MySQL是关系型数据库
SQL历史：
SQL的语句：（SQL 是一门 ANSI 的标准计算机语言（结构化查询语言），用来访问和操作数据库系统，一定要记住，SQL 对大小写不敏感！，一般规定关键字大写。）
具体介绍可参考下面地址：/sql/sql_intro.asp
SQL语句分类：
SQL 中最重要的 DDL 语句:
CREATE DATABASE 创建新数据库名 【default charset='utf8'];没有编码，1，有默认走默认，2，找配置文件 ，3，默认编码（拉丁文编码，中文报错） /*指定编码，(ststem cls ”清屏“)/
增加数据库
进入增加数据库进行查看(use 数据库名称）
删除数据库：
create database db_nhjc default charset="utf8";/*创建可以使用中文数据库db_nhjc/
数据库，一般存在5种约束
MySQL数据类型
Number 类型：
这些整数类型拥有额外的选项 UNSIGNED。通常，整数可以是负数或正数。如果添加 UNSIGNED 属性，那么范围将从 0 开始，而不是某个负数。
创建表
create table t_user (# 定义表的结构字段名称1 字段1类型 [约束条件,]字段名称2 字段2类型 [约束条件,]字段名称3 字段3类型 [约束条件,]...字段名称n 字段n类型 [约束条件]);
下面说一个例子来展示单表的增删查改
首先我们先创建库“ db_mingzhu”（MySQL本身的四个库，小白的我们不要乱动），在库中创建四张表 t_sanguo t_shuihuo t_xiyou t_honglou。并添加相应的人物。
create database db_mingzhu default charset="utf8";USE db_mingzhuCREATE TABLE t_sanguo ( id int primary key auto_increment comment '用户主键',name varchar(20) not null unique comment '用户名称', feeling varchar(20), factions varchar(20));INSERT INTO t_sanguo VALUES(NULL,"曹操","宁教我负天下人，休教天下人负我","魏");INSERT INTO t_sanguo VALUES(NULL,"刘备","勿以恶小而为之，勿以善小而不为","蜀");INSERT INTO t_sanguo VALUES(NULL,"孙权","足下不死，孤不得安！","吴");INSERT INTO t_sanguo VALUES(NULL,"诸葛亮","鞠躬尽瘁死而后已","蜀");INSERT INTO t_sanguo VALUES(NULL,"司马懿","为人者，有大度成大器矣！","魏");INSERT INTO t_sanguo VALUES(NULL,"周瑜","将者贵在知敌虚实，而后避实而击虚。","吴");
现象：
水浒：（其他表相同，小编就不一一操作了）
CREATE TABLE t_shuihuo ( id int primary key auto_increment comment '用户主键',name varchar(20) not null unique comment '用户名称', nickname varchar(20) );INSERT INTO t_shuihuo VALUES(NULL,"九纹龙","史进");INSERT INTO t_shuihuo VALUES(NULL,"神机军师","朱武");INSERT INTO t_shuihuo VALUES(NULL,"跳涧虎","陈达");INSERT INTO t_shuihuo VALUES(NULL,"白花蛇","杨春");INSERT INTO t_shuihuo VALUES(NULL,"花和尚","鲁智深");INSERT INTO t_shuihuo VALUES(NULL,"打虎将","李忠");INSERT INTO t_shuihuo VALUES(NULL,"小霸王","周通");INSERT INTO t_shuihuo VALUES(NULL,"豹子头","林冲");INSERT INTO t_shuihuo VALUES(NULL,"小旋风","柴进");INSERT INTO t_shuihuo VALUES(NULL,"旱地忽律","朱贵");INSERT INTO t_shuihuo VALUES(NULL,"摸着天","杜迁");INSERT INTO t_shuihuo VALUES(NULL,"云里金刚","宋万");INSERT INTO t_shuihuo VALUES(NULL,"青面兽","杨志");INSERT INTO t_shuihuo VALUES(NULL,"急先锋","索超");INSERT INTO t_shuihuo VALUES(NULL,"美髯公","朱仝");INSERT INTO t_shuihuo VALUES(NULL,"插翅虎","雷横");INSERT INTO t_shuihuo VALUES(NULL,"赤发鬼","刘唐");INSERT INTO t_shuihuo VALUES(NULL,"智多星","吴用");INSERT INTO t_shuihuo VALUES(NULL,"立地太岁","阮小二");INSERT INTO t_shuihuo VALUES(NULL,"短命二郎","阮小五");INSERT INTO t_shuihuo VALUES(NULL,"活阎王","阮小七");INSERT INTO t_shuihuo VALUES(NULL,"入云龙","公孙胜");INSERT INTO t_shuihuo VALUES(NULL,"白日鼠","白胜");INSERT INTO t_shuihuo VALUES(NULL,"操刀鬼","曹正");INSERT INTO t_shuihuo VALUES(NULL,"及时雨","宋江");INSERT INTO t_shuihuo VALUES(NULL,"铁扇子","宋清");INSERT INTO t_shuihuo VALUES(NULL,"行者","武松");INSERT INTO t_shuihuo VALUES(NULL,"菜园子","张青");INSERT INTO t_shuihuo VALUES(NULL,"金眼彪","施恩");INSERT INTO t_shuihuo VALUES(NULL,"毛头星","孔明");INSERT INTO t_shuihuo VALUES(NULL,"独火星","孔亮");INSERT INTO t_shuihuo VALUES(NULL,"锦毛虎","燕顺");INSERT INTO t_shuihuo VALUES(NULL,"矮脚虎","王英");INSERT INTO t_shuihuo VALUES(NULL,"白面郎君","郑天寿");INSERT INTO t_shuihuo VALUES(NULL,"小李广","花荣");INSERT INTO t_shuihuo VALUES(NULL,"镇三山","黄信");INSERT INTO t_shuihuo VALUES(NULL,"霹雳火","秦明");INSERT INTO t_shuihuo VALUES(NULL,"小温侯","吕方");INSERT INTO t_shuihuo VALUES(NULL,"赛仁贵","郭盛");INSERT INTO t_shuihuo VALUES(NULL,"石将军","石勇");INSERT INTO t_shuihuo VALUES(NULL,"催命判官","李立");INSERT INTO t_shuihuo VALUES(NULL,"混江龙","李俊");INSERT INTO t_shuihuo VALUES(NULL,"出洞蛟","童威");INSERT INTO t_shuihuo VALUES(NULL,"翻江蜃","童猛");INSERT INTO t_shuihuo VALUES(NULL,"病大虫","薛永");INSERT INTO t_shuihuo VALUES(NULL,"船伙儿","张横");INSERT INTO t_shuihuo VALUES(NULL,"神行太保","戴宗");INSERT INTO t_shuihuo VALUES(NULL,"浪里白条","张顺");INSERT INTO t_shuihuo VALUES(NULL,"拼命三郎","石秀");INSERT INTO t_shuihuo VALUES(NULL,"浪子","燕青");
修改 UPDATE
select * from 表名称;慎用，重新加载表#update 表名称 set 字段1=新值 [, 字段2=新值 ...] where 条件update 表名称 set 字段 = 修改值 ; 指定字段修改，改一字段列update 表名称 set 字段= age + 1 WHERE id = 6; 指定必须是int类型，进行加减，（WHERE id ）按照id“字段”主键约束给字段进行修改UPDATE 表名称 set 字段="120" where age >= 18; where后可以使用">=" "!=" 等
（记对刷新查看）
删除 delete
# delete from 表名称 where 条件;delete from 表名称 where id = 14; 指定id字段进行删除truncate 表名称;-- 慎用！！！ 实例：delete from t_sanguo where id = 1; -- 删除id1
查询
# select * from 表名称select * from t_user; -- 查看一个表全部“*”代表全部-- 查询固定的列select id from t_user; --查看单个字段元素select id, name from t_user; --查看多个字段列元素SELECT * from t_user where id = 1; -- 查看id=1的元素SELECT * from t_user where age > 15; -- 查看＞15的元素SELECT * FROM t_user where age >= 18 or id = 4; -- 也可以使用关联语句SELECT * from t_user where id != 1;SELECT * from t_user where id <> 1; -- <> 作用与 != 相同SELECT * FROM t_user WHERE birthday is null; -- 查询空和非空SELECT * from t_user where birthday IS NOT NULL;
修改表列类型：
