Question

我正在尝试在oracle 11g中创建一个学校注册系统的对象关系数据库，我的sql代码如下。我正在尝试编写一个查询，提供课程名称和在该课程中注册的学生。但是当我尝试添加另一个化学类时，id为101.我收到一个错误。这是因为我已经将courseID作为主键，所以我不能插入多个课程的课程ID？所以任何人都可以告诉我如何创建具有相同ID但不同学生ID的多个化学插入语句？

CREATE TYPE Student_objtyp AS OBJECT (
  FName         VARCHAR2(20),
  LName         VARCHAR2(20),
  StudentID     NUMBER
  ); 
/

CREATE TABLE Student_objtab OF Student_objtyp (StudentID PRIMARY KEY)
  OBJECT IDENTIFIER IS PRIMARY KEY;

CREATE TYPE Course_objtyp AS OBJECT (
  CourseName VARCHAR(20),
  CourseID NUMBER,
  StudentID REF Student_objtyp
  );
/

CREATE TABLE Course_objtab OF Course_objtyp (
  PRIMARY KEY (CourseID),
  FOREIGN KEY (StudentID) REFERENCES Student_objtab)
  OBJECT IDENTIFIER IS PRIMARY KEY;


INSERT INTO Student_objtab VALUES('bill','smitts',1);
INSERT INTO Student_objtab VALUES('bob','jo',2);


INSERT INTO Course_objtab
SELECT 'Chemistry',101,
REF(S)
FROM Student_objtab S
WHERE S.StudentID = 1;

INSERT INTO Course_objtab
SELECT 'Chemistry',101,
REF(S)
FROM Student_objtab S
WHERE S.StudentID = 2;

INSERT INTO Course_objtab
SELECT 'Physics',201,
REF(S)
FROM Student_objtab S
WHERE S.StudentID = 1;

select c.CourseName, c.StudentID
from Course_objtab c;

Answer 1

您需要花一些时间考虑数据库的结构。根据您的描述，您至少需要三张桌子。课程，包括PK course_id，学生，PK student_id和注册，使用外键course_id和student_id，引用各自的表格。

Answer 2

此设计违反了数据库规范化规则。课程应该只保留课程的信息，而不是学生注册课程的学生。 IMO应该至少有一个ENROLLMENT表，引用COURSE和STUDENT。这被称为＆＃34;联合表＆＃34;。

我按如下方式对其进行建模：

员工 - 有关员工（教师/教授等）的信息学生 - 有关学生的信息课程 - 有关可授课的课程的信息 CLASS - 有关课程特定实例的信息，包括课程开会的日期/时间，地点以及教授课程的工作人员。 CLASS_ENROLLMENT - 将学生与特定的CLASS联系起来。

这里可能还有一些关于ROOM和ROOM_SCHEDULE的内容，也许还有一个Academic_CALENDAR。

祝你好运。

Answer 3

由于您的course_objtab表包含在课程中注册的学生，因此PK可能应该是courseID和StudentID：

import collections
import contextlib
import threading

lock = threading.Lock()

wait_tracker = collections.defaultdict(lambda: (False, 0, threading.Condition(lock)))

@contextlib.contextmanager
def critical(bar):
    with lock:
        busy, waiters, condition = wait_tracker[bar]
        if busy:
            # Someone with the same bar value is in the critical section.

            # Record that we're waiting.
            waiters += 1
            wait_tracker[bar] = busy, waiters, condition

            # Wait for our turn.
            while wait_tracker[bar][0]:
                condition.wait()

            # Record that we're not waiting any more.
            busy, waiters, condition = wait_tracker[bar]
            waiters -= 1

        # Record that we're entering the critical section.
        busy = True
        wait_tracker[bar] = busy, waiters, condition
    try:
        # Critical section runs here.
        yield
    finally:
        with lock:
            # Record that we're out of the critical section.
            busy, waiters, condition = wait_tracker[bar]
            busy = False
            if waiters:
                # Someone was waiting for us. Tell them it's their turn now.
                wait_tracker[bar] = busy, waiters, condition
                condition.notify()
            else:
                # No one was waiting for us. Clean up a bit so the wait_tracker
                # doesn't grow forever.
                del wait_tracker[bar]

对象关系数据库主键

3 个答案: