忘记mysql 的root 密码：
先确认已经杀掉mysqld 进程了，然后执行这个
/usr/bin/safe_mysqld --skip-grant-tables &
再这样登录
mysql -h 192.168.1.2 -u root
上边的192.168.1.2 是cloud 的mysqld 运行机器，你换成自己的，这样登录上
去，就可以修改密码了。
修改密码
1.mysql -h hostname –u root 命令登录到mysqld server 用grant 命令改变口令:
Grant all on *.* to root indentified by "111111" |||||||| grant all on *.* to root@192.168.1.1 indentified by '';
2. mysqladmin -u 用户名-p 旧密码password 新密码
3.显示限制行数
select * from databasename.tablename limit begin,countfoyouwant;
4.alter table tablename change[drop,add] columname columname atrributes;
5.update tablename set attr2=if(attr1=valu1,valu2,valu3) ……;
6.delete from tablename;
7.insert into tablename values(……);
8.select * from (select * from table1 where ……) tm where……//嵌套查询
9. select case when b<0 then ''
when b between 5 and 38 then ''
end from tablename //case语句的使用注case后不能加参数
10.select * from tablea where IF((select COUNT(*) from b)>100,a,b)//条件语句中可以加入if语句进行嵌套
11.strname<>'' <===|||===> strname is not NULL
12.strname like '%%' 不能查出空值 strname is NULL
13. select count(*) from b where …… group by attr1 having count(*) <10;