Question

我正在尝试创建具有特定限制的表，并且我不允许使用触发器。

我正在使用Oracle SQL。

限制是：

每个课程ID只有1个课程
学生最多允许4门课程
课程最多允许25名学生
每门课程都是1位讲师
每个学生只有一个专业

Bolded 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 );

<强>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

制定约束的简单解决方案是：

将整数STUDENT_LFDNR和COURSE_LFDNR添加到STU_CRSE

在（STUDENT_ID，STUDENT_LFDNR），（COURSE_ID，COURSE_LFDNR）上添加唯一键

在STUDENT_LFDNR上添加constarint（＆gt; 0＆amp;＆lt; = 4）

在COURSE_LFDNR上添加约束（＆gt; 0＆amp;＆lt; = 25）

但与此合作会很痛苦......

基于FK关系约束表

2 个答案: