基于FK关系约束表

Question

我正在尝试创建具有特定限制的表，并且不允许使用触发器。

我使用的是Oracle SQL。

限制是：

1. 每个课程ID只有1节课
2. 学生最多可选修4门课程
3. 课程最多允许25名学生
4. 每门课程由1名讲师教授
5. 每个学生只有一个专业

粗体2和3是我遇到问题的地方。

CREATE TABLE STUDENT(
  STUDENT_ID NUMERIC(9),
  STUDENT_NAME VARCHAR(32) NOT NULL,
  STUDENT_ADDRESS VARCHAR(50),
  MAJOR VARCHAR(4),
  CONSTRAINT student_id_pk PRIMARY KEY(STUDENT_ID)
);
CREATE TABLE COURSE(
  COURSE_ID VARCHAR(6),
  COURSE_TITLE VARCHAR(32) NOT NULL,
  INSTRUCTOR_ID NUMERIC(3) UNIQUE,
  CONSTRAINT course_id_pk PRIMARY KEY(COURSE_ID),
  CONSTRAINT instructor_id_fk FOREIGN KEY (INSTRUCTOR_ID) REFERENCES INSTRUCTOR(INSTRUCTOR_ID)
);
CREATE TABLE INSTRUCTOR(
  INSTRUCTOR_ID NUMERIC(3),
  INSTRUCTOR_NAME VARCHAR(50) NOT NULL,
  INSTRUCTOR_OFFICE VARCHAR(4),
  CONSTRAINT instructor_id_pk PRIMARY KEY(INSTRUCTOR_ID)
);
CREATE TABLE STU_CRSE(
  STUDENT_ID NUMERIC (9),
  COURSE_ID VARCHAR(6),
  GRADE CHAR(1),
  CONSTRAINT grade_range CHECK(GRADE IN ('A','B','C','D','F')),
  CONSTRAINT stu_crs_pk PRIMARY KEY (STUDENT_ID,COURSE_ID),
  CONSTRAINT crs_fk FOREIGN KEY (COURSE_ID) REFERENCES COURSE(COURSE_ID),
  CONSTRAINT str_fk FOREIGN KEY (STUDENT_ID) REFERENCES STUDENT(STUDENT_ID),
--
--Below are the constraints I'm having trouble with.
--
  CONSTRAINT stu_limit CHECK (COUNT(STU_CRSE.STUDENT_ID)<5),
  CONSTRAINT stu_crse_limit CHECK (count(STU_CRSE.STUDENT_ID,STU_CRSE.COURSE_ID)<26)
);

Answer 1

您可以尝试：

CREATE MATERIALIZED VIEW LOG ON STU_CRSE
   WITH SEQUENCE, ROWID(course_id, student_id)
   INCLUDING NEW VALUES;
CREATE MATERIALIZED VIEW STU_CRSE__NUM_STUDENTS__MV
   BUILD IMMEDIATE
   REFRESH FAST ON COMMIT
   AS SELECT COURSE_ID,
             COUNT( STUDENT_ID ) AS num_students
      FROM   STU_CRSE
      GROUP BY COURSE_ID;
ALTER TABLE STU_CRSE__NUM_STUDENTS__MV
  ADD CONSTRAINT STU_CRSE__NUM_STU__MV__COUNT CHECK ( num_students <= 25 );
CREATE MATERIALIZED VIEW STU_CRSE__NUM_COURSES__MV
   BUILD IMMEDIATE
   REFRESH FAST ON COMMIT
   AS SELECT STUDENT_ID,
             COUNT( COURSE_ID ) AS num_courses
      FROM   STU_CRSE
      GROUP BY STUDENT_ID;
ALTER TABLE STU_CRSE__NUM_COURSES__MV
  ADD CONSTRAINT STU_CRSE__NUM_CRS__MV__COUNT CHECK ( num_courses <= 4 );

测试：

INSERT INTO STU_CRSE
SELECT 1, LEVEL, 'A' FROM DUAL CONNECT BY LEVEL <= 4;
4 rows inserted.
COMMIT;
Commit complete.
INSERT INTO STU_CRSE VALUES (1, 5, 'A' );
1 row inserted.
COMMIT;
Error report -
SQL Error: ORA-12048: error encountered while refreshing materialized view "TEST"."STU_CRSE__NUM_COURSES__MV"
ORA-02290: check constraint (TEST.STU_CRSE__NUM_CRS__MV__COUNT) violated

Answer 2

一个简单的约束解决方案是：

将整数STUDENT_LFDNR和COURSE_LFDNR添加到STU_CRSE

在（STUDENT_ID、STUDENT_LFDNR）、（COURSE_ID、COURSE_LFDNR

在STUDENT_LFDNR（>0&<=4）上添加常量打印

在COURSE_LFDNR（>0&<=25）上添加约束

但与之合作将是痛苦的。。。