方法：

1. 删除所有外键约束

2. drop表

3. 添加外键约束
代码使用powerdesign生成

alter table Da_pic drop constraint FK_DA_PIC_REFERENCE_DA_PICSU; drop table Da_pic cascade constraints; drop table Da_picsubject cascade constraints; create table Da_pic ( ID VARCHAR2(200) not null, no VARCHAR2(200), subjiectid VARCHAR2(200), Name VARCHAR2(400), UploadTime DATE, UserId VARCHAR2(200), picdate DATE, place VARCHAR2(200), people VARCHAR2(200), event VARCHAR2(200), background VARCHAR2(200), cameramen VARCHAR2(200), serial INTEGER, IsEffect VARCHAR2(200), constraint PK_DA_PIC primary key (ID) ); create table Da_picsubject ( ID VARCHAR2(200) not null, no VARCHAR2(200), title VARCHAR2(200), year VARCHAR2(200), type VARCHAR2(200), gdtime DATE, iseffect VARCHAR2(200), seiral INTEGER, constraint PK_DA_PICSUBJECT primary key (ID) ); alter table Da_pic add constraint FK_DA_PIC_REFERENCE_DA_PICSU foreign key (subjiectid) references Da_picsubject (ID);