--1 创建备份表

drop table contract_kangjia_back;

create table contract_kangjia_back

as

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;