相對MySQL數據庫

Question

我有一個MySQL數據庫表，它內置如下。 類別下方的數字表示該類別的「級別」，例如高，中或低，0表示不在該類別。

我需要建立另一個表來保存每個類的作業分配，但是我對於如何構建該表有點遺憾，特別是表示行的確切列必須是什麼，因爲每個類沒有特定的東西表示它。

Answer 1

一個適當規範化的結構將有一個單獨的課程表，每個表都有一個ID，另一個表通過包含學生ID，課程ID和級別將學生放入課程。

CREATE TABLE students (
    id INT NOT NULL PRIMARY KEY AUTO_INCREMENT, 
    username VARCHAR(64) NOT NULL, 
    password VARCHAR(64), 
    email VARCHAR(...) 
    UNIQUE KEY (username) 
); 

CREATE TABLE courses (
    id INT NOT NULL PRIMARY KEY AUTO_INCREMENT, 
    name VARCHAR(64) NOT NULL 
); 

/* If a record doesn't exist for a course and student, 
    the student isn't enrolled in that course. Otherwise, 
    the level is defined here */ 
CREATE TABLE enrollments (
    id INT NOT NULL PRIMARY KEY, 
    student_id INT NOT NULL, 
    course_id INT NOT NULL, 
    level INT NOT NULL, 
    /* Each student may be enrolled only once per course */ 
    UNIQUE KEY (student_id, course_id), 
    FOREIGN KEY (student_id) REFERENCES students (id), 
    FOREIGN KEY (course_id) REFERENCES courses (id) 
); 

最後的話，您可以爲每門課程指派的任務表：

CREATE TABLE assignments (
    id INT NOT NULL PRIMARY KEY, 
    course_id INT NOT NULL, 
    description TEXT 
    /*... other columns related to the assignment as necessary*/ 
); 

併爲學生如果需要完成的任務：

CREATE TABLE student_assignments (
    student_id INT NOT NULL, 
    assignment_id INT NOT NULL, 
    assignment_body TEXT, /* or whatever... */ 
    /* Or to track when completed */ 
    submitted_timestamp TIMESTAMP, 
    PRIMARY KEY (student_id, assignment_id), 
    FOREIGN KEY (assignment_id) REFERENCES assignments (id), 
    FOREIGN KEY (student_id) REFERENCES students (id) 
);