##MySQL数据库SQL(Structured Query Language)结构化查询语言常用基本操作:
/*DDL(Data Definition Language)数据定义语言*/
##创建数据库:
create database ‘数据库名称’ character utf8;
##删除数据库:
drop database ‘数据库名称’;
##显示所有数据库:
show databases;
##使用数据库
use ‘数据库名称’;
##确定当前使用数据库:
select dababase();
##显示数据库中某表结构
desc ‘表名’;
##显示某表的创建语句
show create table ‘表名’;

##创建表:
create table ‘表名’(
‘列名’ ‘列描述’,
‘列名’ ‘列描述’,
‘列名’ ‘列描述’);
##带主键且自增长的表
create table ‘表名’(
‘列名’ ‘列描述’ primary key auto_increment,
‘列名’ ‘列描述’,
‘列名’ ‘列描述’);
##删除表:
drop table ‘表名’;
##修改表:
alter table ‘旧表名’ rename ‘新表名’;

##添加字段
alter table ‘表名’ add column ‘列名’ ‘列描述’;
##修改字段
alter table ‘表名’ change ‘旧列名’ ‘新列名’ ‘新列描述’;
##删除字段
alter table ‘表名’ drop column ‘列名’;

/*DML(Data Manipulation Language)数据操作语言*/
##录入数据
insert into ‘表名’(‘字段名,字段名…’) values(‘对应值,对应值…’);
insert into ‘表名’ values(‘对应值,对应值…’);
##更新数据
update ‘表名’ set ‘字段名’=’字段值’,’字段名’=’字段值’… where ‘字段名’=’字段值’;
update ‘表名’ set ‘字段名’=’字段值’,’字段名’=’字段值’…;
##删除数据
delete from ‘表名’;
delete from ‘表名’ where ‘字段名’=’字段值’;
/*DQL(Data Queries Language)数据查询语言*/
##查询所有
select * from ‘表名’;
##查询需要的
select ‘字段名’,’字段名’… from ‘表名’;
##别名查询
select ‘字段名’,concat(‘字段名’,’字段名’) [as] ‘别名’ from ‘表名’;
##where查询
select * from ‘表名’ where ‘字段名’ like “_’值’%”
##聚合查询
select count(*) from ‘表名’; ##查询记录数
select ‘字段名’ from ‘表名’ order by ‘字段名’ desc; ##依降序查询
select distinct ‘字段名’ from ‘表名’ order by ‘字段名’ asc; ##去重复依升序查询
##分组查询
select avg(‘字段名’) from ‘表名’ group by ‘字段名’;
select avg(字段名) as ‘别名’,’别名’ from ‘字段名’ group by ‘字段名’ having ‘字段名’>0;

/*DCL(Data Control Language)数据控制语言*/

/*约束*/
##主键约束
alter table ‘表名’ add constraint primary key(‘字段名’);
##唯一约束
alter table ‘表名’ add constraint unique(‘字段名’);
##外键约束
alter table ‘表名’ add constraint foreign key(‘外键字段名’) references ‘主表’(‘主键字段名’);