--1 创建备份表drop table contract_kangjia_back;create table contract_kangjia_backas select *　from contract_kangjia;--2 将原有表的数据删除delete from contract_kangjia;--3 改变原有表的数据结构alter table contract_kangjia modify sell_money  number(10,5) ;--4 将原有表的数据插入新的表insert into contract_kangjia  (id, busiman_name, sell_date, product_type, sell_money)  select  id, busiman_name, sell_date, product_type, sell_money     from contract_kangjia_back;