当primary用于其他表时，如何防止在表中输入值？

Question

我必须构建和填充超类型-子类型关系，但我无法让它按应有的方式工作。基本上 PERSON 表是表 STUDENT 和 TEACHER（子类型）的超类型。但是一个人可以是学生也可以是老师。

属性：

PERSON(p_id, name, dob)

学生（s_id、p_id、年级）

教师（t_id，p_id，电话）

---

学生和老师都应该有姓名和出生日期以及作为外键的 p_id，但如果它存在于一个表上，则不应在另一个表上

CREATE TABLE PERSON ( -- SUPERTYPE
    p_id NUMBER(2) CONSTRAINT c1 PRIMARY KEY,
    name CHAR(15),
    dob DATE
);

CREATE TABLE STUDENT ( -- SUBTYPE
    s_id NUMBER(2) CONSTRAINT c2 PRIMARY KEY,
    p_id_fk,
    grade CHAR(1),
    FOREIGN KEY (p_id_fk) REFERENCING PERSON (p_id)
);

CREATE TABLE TEACHER( -- SUBTYPE
    t_id NUMBER(4) CONSTRAINT c3 PRIMARY KEY,
    p_id_fk,
    tel CHAR(8),
    FOREIGN KEY (p_id_fk) REFERENCING PERSON (p_id)
);

INSERT INTO PERSON VALUES (11, 'John', to_date('12/12/12', 'dd/mm/yy'));
INSERT INTO PERSON VALUES (22, 'Maria', to_date('01/01/01', 'dd/mm/yy'));
INSERT INTO PERSON VALUES (33, 'Philip', to_date('02/02/02', 'dd/mm/yy'));

INSERT INTO STUDENT VALUES (98, 11, 'A');

INSERT INTO TEACHER VALUES (1234, 11, 14809510);

如何防止 Person 11 (John) 出现在两个表中？

Answer 1

一种选择是使用数据库触发器，每个表一个（STUDENT 和TEACHER）；它们看起来一样：

触发STUDENT:

SQL> create or replace trigger trg_bi_stu
  2    before insert on student
  3    for each row
  4  declare
  5    l_cnt number;
  6  begin
  7    -- inserting into STUDENT: check whether that person exists in TEACHER table
  8    select count(*)
  9      into l_cnt
 10      from teacher
 11      where p_id_fk = :new.p_id_fk;
 12
 13    if l_cnt > 0 then
 14       raise_application_error(-20001, 'That person is a teacher; can not be a student');
 15    end if;
 16  end;
 17  /

Trigger created.

触发TEACHER:

SQL> create or replace trigger trg_bi_tea
  2    before insert on teacher
  3    for each row
  4  declare
  5    l_cnt number;
  6  begin
  7    -- inserting into TEACHER: check whether that person exists in STUDENT table
  8    select count(*)
  9      into l_cnt
 10      from student
 11      where p_id_fk = :new.p_id_fk;
 12
 13    if l_cnt > 0 then
 14       raise_application_error(-20001, 'That person is a student; can not be a teacher');
 15    end if;
 16  end;
 17  /

Trigger created.

SQL>

测试：

SQL> INSERT INTO STUDENT VALUES (98, 11, 'A');

1 row created.

SQL>
SQL> INSERT INTO TEACHER VALUES (1234, 11, 14809510);
INSERT INTO TEACHER VALUES (1234, 11, 14809510)
            *
ERROR at line 1:
ORA-20001: That person is a student; can not be a teacher
ORA-06512: at "SCOTT.TRG_BI_TEA", line 11
ORA-04088: error during execution of trigger 'SCOTT.TRG_BI_TEA'


SQL>

Answer 2

存在四种方式如何将继承映射到关系数据库。

您正在使用最奇特的第三个选项，这是导致问题的原因。考虑切换到其他选项之一作为解决方案。

前三个很好理解并记录在案，page 提供了有用的链接。

基本上可以映射

1) 一张表中的所有类

2) 为所有具体类使用一张表

3) 为 aech 类定义一张表

所有这些选项都存在一些问题，无论是过度连接还是禁用约束（例如，您不能在选项 1 中定义不可为空的列），因此为了完整性，选项 4）是 不要在关系数据库中使用继承。

您已尝试实现选项 3)，但问题是所有表都必须继承相同的主键（以强制 1:1 关系）并将此 主键用作 外键。

这里是您示例的所有选项的概述

-- 1) single table
CREATE TABLE PERSON (  
    p_id NUMBER(2) CONSTRAINT pers_pk PRIMARY KEY,
    name CHAR(15),
    dob DATE,
    grade CHAR(1),
    tel CHAR(8),
    person_type VARCHAR2(10) CONSTRAINT pers_type CHECK  (person_type in ('STUDENT','TEACHER'))
);

-- 2) table per concrete class
CREATE TABLE STUDENT (  
    p_id NUMBER(2) CONSTRAINT stud_pk PRIMARY KEY,
    name CHAR(15),
    dob DATE,
    grade CHAR(1) 
);

CREATE TABLE TEACHER(  
    p_id NUMBER(2) CONSTRAINT tech_pk PRIMARY KEY,
    name CHAR(15),
    dob DATE,
    tel CHAR(8)
);

-- 3) table per class
CREATE TABLE PERSON (  
    p_id NUMBER(2) CONSTRAINT pers_pk PRIMARY KEY,
    name CHAR(15),
    dob DATE
);

CREATE TABLE STUDENT (  
    p_id NUMBER(2) CONSTRAINT stud_pk PRIMARY KEY,
    grade CHAR(1),
    FOREIGN KEY (p_id) REFERENCING PERSON (p_id)
);

CREATE TABLE TEACHER( 
    p_id NUMBER(2) CONSTRAINT tech_pk PRIMARY KEY,
    tel CHAR(8),
    FOREIGN KEY (p_id) REFERENCING PERSON (p_id)
);

INSERT INTO PERSON (P_ID, NAME, DOB) VALUES (11, 'John', to_date('12/12/2012', 'dd/mm/yyyy'));
INSERT INTO PERSON (P_ID, NAME, DOB) VALUES (22, 'Maria', to_date('01/01/2001', 'dd/mm/yyyy'));
INSERT INTO PERSON (P_ID, NAME, DOB) VALUES (33, 'Philip', to_date('02/02/2002', 'dd/mm/yyyy'));

INSERT INTO STUDENT (P_ID, GRADE) VALUES (11, 'A');
INSERT INTO TEACHER (P_ID, TEL) VALUES (11, 14809510);

Answer 3

使用具有适当约束的物化视图来检查诸如此类的复杂需求。

例如，让我们创建表和物化视图，将数据添加到表中，然后刷新 MV：

CREATE TABLE PERSON ( -- SUPERTYPE
    p_id NUMBER(2) CONSTRAINT c1 PRIMARY KEY,
    name CHAR(15),
    dob DATE
);

CREATE TABLE STUDENT ( -- SUBTYPE
    s_id NUMBER(2) CONSTRAINT c2 PRIMARY KEY,
    p_id_fk,
    grade CHAR(1),
    FOREIGN KEY (p_id_fk) REFERENCING PERSON (p_id)
);

CREATE TABLE TEACHER( -- SUBTYPE
    t_id NUMBER(4) CONSTRAINT c3 PRIMARY KEY,
    p_id_fk,
    tel CHAR(8),
    FOREIGN KEY (p_id_fk) REFERENCING PERSON (p_id)
);

CREATE MATERIALIZED VIEW PERSON_MV
  REFRESH COMPLETE
  AS SELECT p.P_ID,
            s.S_ID,
            t.T_ID
       FROM PERSON p
       LEFT OUTER JOIN STUDENT s
         ON s.P_ID_FK = p.P_ID
       LEFT OUTER JOIN TEACHER t
         ON t.P_ID_FK = p.P_ID;

-- Add constraint to the table underlying the MV

ALTER MATERIALIZED VIEW PERSON_MV
  ADD CONSTRAINT PERSON_MV_CK1
    CHECK( (S_ID IS NULL AND       -- either both are NULL
            T_ID IS NULL) OR
           ( (S_ID IS NULL OR      -- or only one is NULL
              T_ID IS NULL) AND
             (S_ID IS NOT NULL OR
              T_ID IS NOT NULL)));

INSERT ALL
  INTO PERSON (P_ID, NAME, DOB) VALUES (11, 'John', to_date('12/12/2012', 'dd/mm/yyyy'))
  INTO PERSON (P_ID, NAME, DOB) VALUES (22, 'Maria', to_date('01/01/2001', 'dd/mm/yyyy'))
  INTO PERSON (P_ID, NAME, DOB) VALUES (33, 'Philip', to_date('02/02/2002', 'dd/mm/yyyy'))
SELECT * FROM DUAL;

COMMIT;

INSERT INTO STUDENT VALUES (98, 11, 'A');

COMMIT;

BEGIN
  DBMS_MVIEW.REFRESH('PERSON_MV', 'C', '', TRUE, FALSE, 0, 0, 0, FALSE, FALSE);
END;
/

SELECT *
  FROM PERSON_MV;

注意添加到物化视图的约束：

ALTER MATERIALIZED VIEW PERSON_MV
  ADD CONSTRAINT PERSON_MV_CK1
    CHECK( (S_ID IS NULL AND       -- either both are NULL
            T_ID IS NULL) OR
           ( (S_ID IS NULL OR      -- or only one is NULL
              T_ID IS NULL) AND
             (S_ID IS NOT NULL OR
              T_ID IS NOT NULL)));

此约束允许数据存在于：

• 存在 PERSON 行，但不存在相关的 STUDENT 或 TEACHER 行
• PERSON 行与任何一个相关的 STUDENT 或 TEACHER 行存在，但不能同时存在

所以当我们从物化视图中执行最终的 SELECT 时，我们得到：

P_ID  S_ID  T_ID
11     98    - 
33     -     - 
22     -     - 

现在让我们修改上面的脚本，在INSERT INTO STUDENT之后添加以下内容：

INSERT INTO TEACHER VALUES (1234, 11, 14809510);

COMMIT;

如果我们重新运行整个脚本，我们发现当调用 DBMS_MVIEW.REFRESH 刷新我们得到的物化视图时：

ORA-12008: error in materialized view or zonemap refresh path ORA-06512: at "SYS.DBMS_SNAPSHOT_KKXRCA", line 3012
ORA-06512: at "SYS.DBMS_SNAPSHOT_KKXRCA", line 2424
ORA-06512: at "SYS.DBMS_SNAPSHOT_KKXRCA", line 88
ORA-06512: at "SYS.DBMS_SNAPSHOT_KKXRCA", line 253
ORA-06512: at "SYS.DBMS_SNAPSHOT_KKXRCA", line 2405
ORA-06512: at "SYS.DBMS_SNAPSHOT_KKXRCA", line 2968
ORA-06512: at "SYS.DBMS_SNAPSHOT_KKXRCA", line 3255
ORA-06512: at "SYS.DBMS_SNAPSHOT_KKXRCA", line 3287
ORA-06512: at "SYS.DBMS_SNAPSHOT", line 16
ORA-06512: at line 2
ORA-06512: at "SYS.DBMS_SQL", line 1721

这是甲骨文相当冗长的说法，即违反了约束。

See this LiveSQL Oracle session

Answer 4

继@Bob 的物化视图方法之后，在提交时捕获问题的版本可能如下所示：

CREATE MATERIALIZED VIEW LOG ON STUDENT WITH PRIMARY KEY, ROWID;

CREATE MATERIALIZED VIEW LOG ON TEACHER WITH PRIMARY KEY, ROWID;

CREATE MATERIALIZED VIEW PERSON_HACK (p_id_fk, marker, rid) 
BUILD IMMEDIATE 
REFRESH ON COMMIT AS 
SELECT p_id_fk, 1, ROWID FROM STUDENT 
UNION ALL 
SELECT p_id_fk, 2, ROWID FROM TEACHER;

ALTER MATERIALIZED VIEW PERSON_HACK 
ADD CONSTRAINT PERSON_HACK_PK PRIMARY KEY (p_id_fk);

这应该类似于延迟约束，在提交时刷新 MV（并且违反其主键）时出错。使用并发插入，第二个要提交的会话会看到错误。

Live SQL，尽管 MV 似乎有一些问题（在别处报告）。它应该报告约束违规，而不是抛出 ORA-12008。但我目前无法在其他地方进行测试 - SQL Fiddle 或 dbfiddle 都不允许创建 MV。

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当然，如果您还没有学过 MV，那么在作业中使用 MV 可能看起来有点奇怪。似乎更有可能你已经被教导过对象并且作业期待那些 - 即使它们在现实世界中（在数据库中）很少使用，它们似乎无论如何都被教导，以及旧的连接语法和其他不良做法...