再次认识mysql（一）

mysql：管理数据的软件

mysqld.exe：服务器端

mysql.exe:客户端

sql：structured query language  结构化查询语言  分为三个部分 dml ddl dcl

dml：数据操作语言  处理数据

ddl ：数据定义语言  定义和管理数据库

dcl：数据控制语言   授予或者回收访问数据库的特权 对数据库监视  

insert into user（uid,name,age）values(1,'liming',22),(2,"ni cheng",21);  插入必是一整行

delete from user where uid=2;     删除必是一整行

update user set   name='wangrui',age=21  where uid=4;

select uid from user where uid>=10;

select查询模型   where是表达式 值为真假  列是变量  列可以计算

select uid from user where 1;   //   1为真 取出所有行

select uid from user where uid in(4,10);                  in在某集合中  相当于or

select uid from user where uid  between   4 and 10;     and在某范围中 相当于 and 

select uid from user where uid  not  in(4,10);    

模糊查询  like      select uid from user where name like ‘li%’;  %代表任意字符

                               select uid from user where name like ‘l___’  _代表一个字符 单一字符  

update user  set  uid=floor(uid/10)*10 where uid between 20 and 30;

对查询结果集进行运算

select   uid ,concat('test',substring(name,2))  from user where name like 'li%';