mysql alter 语句用法,添加、修改、删除字段等
//主键549830479

   alter table tabelname add new_field_id int(5) unsigned default 0 not null auto_increment ,add primary key (new_field_id);
//增加一个新列549830479

   alter table t2 add d timestamp;
alter table infos add ex tinyint not null default '0';
//删除列549830479

   alter table t2 drop column c;
//重命名列549830479

   alter table t1 change a b integer;

//改变列的类型549830479

   alter table t1 change b b bigint not null;
alter table infos change list list tinyint not null default '0';

//重命名表549830479

   alter table t1 rename t2;
加索引549830479

   mysql> alter table tablename change depno depno int(5) not null;
mysql> alter table tablename add index 索引名 (字段名1[，字段名2 …]);
mysql> alter table tablename add index emp_name (name);
加主关键字的索引549830479

mysql> alter table tablename add primary key(id);
加唯一限制条件的索引549830479

  mysql> alter table tablename add unique emp_name2(cardnumber);
删除某个索引549830479

   mysql>alter table tablename drop index emp_name;
修改表：549830479

增加字段：549830479

   mysql> ALTER TABLE table_name ADD field_name field_type;
修改原字段名称及类型：549830479

   mysql> ALTER TABLE table_name CHANGE old_field_name new_field_name field_type;
删除字段：549830479

   mysql> ALTER TABLE table_name DROP field_name;