修改
=====
1. 修改表名称
alter table t1 rename to t2;
alter table t1 rename to t2;
2. 改列名,将name改为username,并放在age列后面
alter table t1 change name username string after age;
alter table t1 change name username string after age;
3. 增加列
alter table t1 add columns(sex char(1));
alter table t1 add columns(sex char(1));
4. 重新定义列
alter table t1 replace columns(id int, name string, sex char(1),age int);
alter table t1 replace columns(id int, name string, sex char(1),age int);
