SQL：表或视图不存在，为什么？

Question

这是代码：

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"

所以我搜寻了，但是什么也没找到。 当您以错误的权限调用select时，似乎会发生所有此类错误，但是在CREATE TABLE上的简单调用中却出现了此错误。
因此，我尝试删除它并最终重新创建它，但是没有任何改变。

Answer 1

您在外部约束中引用了未创建的表，因此请更改顺序。

没有外来约束的第一个表和引用这些表的后表

  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

因为您已级联到放置查询中的约束，所以Director_ID，ACTOR_ID和Company_ID的外键约束已受到影响，并且由于这些表也已删除，因此“创建FILM表”查询无法找到其他表来链接FOREIGN KEYS。 您需要自下而上运行CREATE查询，以便最后创建对其他表具有FOREIGN KEYS的FILM表，并重新建立REFERENTIAL KEYS。