SQL :表或视图不存在，为什么？

Question

下面是代码：

DROP TABLE FILM CASCADE CONSTRAINTS; 
DROP TABLE COMPANY CASCADE CONSTRAINTS;
DROP TABLE MAIN_ACTOR CASCADE CONSTRAINTS;
DROP TABLE DIRECTOR CASCADE CONSTRAINTS;

CREATE TABLE FILM (
    Film_ID         NUMBER(4)       PRIMARY KEY,
    Title           VARCHAR2(35)    NOT NULL,
    Year            Date            NOT NULL,
    Language        VARCHAR2(20),
    Director_ID     NUMBER(4)       NOT NULL,       
    Actor_ID        NUMBER(4)       NOT NULL,     
    Company_ID      NUMBER(4)       NOT NULL,       
    Genre           NUMBER(4)       NOT NULL,
    FOREIGN KEY (Director_ID)   REFERENCES  DIRECTOR(Director_ID),
    FOREIGN KEY (Actor_ID)      REFERENCES  MAIN_ACTOR(Main_Actor_ID),
    FOREIGN KEY (Company_ID)    REFERENCES  COMPANY(Company_ID)
);

CREATE TABLE COMPANY (
    Company_ID          NUMBER(4)       PRIMARY KEY,
    Company_Name        VARCHAR2(20)    NOT NULL,
    Company_Country     VARCHAR2(20)    NOT NULL
);

CREATE TABLE MAIN_ACTOR (
    Main_Actor_ID   NUMBER(4)       PRIMARY KEY,
    First_Name      VARCHAR2(20)    NOT NULL,
    Last_Name       VARCHAR2(20)    NOT NULL,
    Birthday        Date            NOT NULL,
    Country         VARCHAR2(20)
);

CREATE TABLE DIRECTOR (
    Director_ID             NUMBER(4)       PRIMARY KEY,
    Director_First_Name     VARCHAR2(20),
    Director_Last_Name      VARCHAR2(20)    NOT NULL,
    Director_BD             Date,            
    Country                 VARCHAR2(20)    NOT NULL
);

我得到的错误是：

Line 6
Error report -
ORA-00942: table or view does not exist
00942. 00000 -  "table or view does not exist"

所以我找了找却什么也没找到。当您使用错误的权限调用select时，所有类似的错误似乎都会发生，但是在这里，对创建表的简单调用，给出了这个错误。

因此，我尝试放弃 it，并最终重新-创建 it，但是没有什么改变。

Answer 1

在外部约束中引用未创建的表，因此更改顺序。

没有外部约束的第一个表和引用这些表的后置表

  DROP TABLE FILM CASCADE CONSTRAINTS; 
  DROP TABLE COMPANY CASCADE CONSTRAINTS;
  DROP TABLE MAIN_ACTOR CASCADE CONSTRAINTS;
  DROP TABLE DIRECTOR CASCADE CONSTRAINTS;

  CREATE TABLE DIRECTOR (
      Director_ID             NUMBER(4)       PRIMARY KEY,
      Director_First_Name     VARCHAR2(20),
      Director_Last_Name      VARCHAR2(20)    NOT NULL,
      Director_BD             Date,            
      Country                 VARCHAR2(20)    NOT NULL
  );

  CREATE TABLE MAIN_ACTOR (
      Main_Actor_ID   NUMBER(4)       PRIMARY KEY,
      First_Name      VARCHAR2(20)    NOT NULL,
      Last_Name       VARCHAR2(20)    NOT NULL,
      Birthday        Date            NOT NULL,
      Country         VARCHAR2(20)
  );

  CREATE TABLE COMPANY (
      Company_ID          NUMBER(4)       PRIMARY KEY,
      Company_Name        VARCHAR2(20)    NOT NULL,
      Company_Country     VARCHAR2(20)    NOT NULL
  );

  CREATE TABLE FILM (
      Film_ID         NUMBER(4)       PRIMARY KEY,
      Title           VARCHAR2(35)    NOT NULL,
      Year            Date            NOT NULL,
      Language        VARCHAR2(20),
      Director_ID     NUMBER(4)       NOT NULL,       
      Actor_ID        NUMBER(4)       NOT NULL,     
      Company_ID      NUMBER(4)       NOT NULL,       
      Genre           NUMBER(4)       NOT NULL,
      FOREIGN KEY (Director_ID)   REFERENCES  DIRECTOR(Director_ID),
      FOREIGN KEY (Actor_ID)      REFERENCES  MAIN_ACTOR(Main_Actor_ID),
      FOREIGN KEY (Company_ID)    REFERENCES  COMPANY(Company_ID)
  );

Answer 2

由于级联到drop查询中的约束，Director_ID、ACTOR_ID和Company_ID的外键约束也受到了影响，而且随着这些表也被删除，表也无法找到链接外键的其他表。您需要从下到上运行创建查询，以便最后创建包含其他表外键的胶片表，并重新建立引用键。