设计一个简单的教师主题学生批量关系数据库的方式是什么？

Question

条件是

1. 许多教师于同一主题的关系，这是一个主题可以由一个以上的教师授课，但一个老师只能教一个主题

2. 许多学生到许多学科的关系，也就是说很多学生可以参加一个共同的学科，一个学生可以参加很多科目。

3. 许多学生对很多批次的关系。

4. 两个批次不能一次保存，所以在批次表中需要一个唯一的日期字段。

5. 许多批次到一个主题关系，即每个批次仅教授一个主题。 但是在其他批次中可以重复上一批中讲授的相同主题。

6. 最后一个情况是给我的问题，那就是很多批次对一个教师的关系， 是一个教师可以在多个批次中教并且每批只有一个教师。

我最初的做法是如下

teacher table 
----------------------- 
id(PK) name email subject_id(FK to subject.id) 



subject table 
----------------------- 
id(PK) name description 



student table 
---------------------- 
id(PK) name location 



batch table 
---------------------- 
id(PK) venue teacher_id(FK to teacher.id) date(unique) 



student-batch table 
----------------------- 
id(PK) batch_id(FK to batch.id) student_id(FK to student.id) 

，并需要得到的信息可以说一批的ID，老师的名字，学生的某一天的名称。

但是，当分配教师批次时，每个批次中只有一个特定的科目正在教授，还有一位教师不能教授多个科目。

Answer 1

你缺少一个表关联科目和学生（每点2）：

// student [student_id] takes subject [subject_id] 
takes(student_id,subject_id) 

注意，每个基地台有关于应用情况的相关声明。使声明为真的行进入表中。请注意，表格定义看起来像是语句的简写。

// teacher [id] named [name] with email [email] teaches subject [subject_id] 
teacher(id,name,email,subject_id) 

// subject [id] named [name] is [description] 
subject(id,name,description) 

// student [id] named [name] lives at [location]) 
student(id,name,location) 

// batch [id] at venue [venue] was taught by teacher [teacher_id] on date [date] 
batch(id,venue,teacher_id,date) 

// student-batch [id] reports student [student_id] being in batch [batch_id] 
student-batch(id,student_id,batch_id) 
CONSTRAINT ?? -- student [student_id] takes the subject that is taught by the teacher of batch [batch_id] 

既然你看起来很难理解这个问题，我将根据我们如何推理表，约束和查询设计来推导它。

要在SQL中表达任何表，约束或查询，我们首先要确定它的语句。然后，我们可以将语句转换为简写。然后我们可以将简写转换为SQL。

一个表包含使其声明为真的行。所以我们通过在SQL中编写表名来获得满足基表语句的行。

通过在SQL中加入语句表，我们得到满足两个语句的AND的行。如果我们希望行满足条件的AND，那么我们在SQL中使用ON或WHERE。对于OR我们使用UNION。对于AND NOT，我们使用EXCEPT/MINUS（或LEFT JOIN成语）。

如果我们希望行满足某些列的某些值，即哪里存在某些列的值（但我们不想要该值），那么我们使用SELECT来删除SQL中的列。我们可以在我们的声明中使用FOR，重新列出我们保留的列。 FOR SOME或THERE所有列的存在都不能用SQL编写，但如果我们想知道是否有行满足语句，那么在SQL中，我们在语句的SELECT周围使用EXISTS作为条件。

// student [student_id] takes the subject that is taught by the teacher of batch [batch_id] 
FOR SOME name, email, venue, date, takes.student_id, ... (
    student [takes.student_id] takes subject [takes.subject_id] 
AND teacher [teacher.id] named [name] with email [email] teaches subject [teacher.subject_id] 
AND batch [batch.id] at venue [venue] was taught by teacher [batch.teacher_id] on date [date] 
AND [takes.subject_id] = [teacher.subject_id] 
AND [teacher.id] = [batch.teacher_id] 
AND [student_id] = [takes.student_id] 
AND [batch_id] = [batch.id]) 

简写：

// student [student_id] takes the subject that is taught by the teacher of batch [batch_id] 
FOR SOME ... (
    takes(takes.student_id,takes.subject_id) 
AND teacher(teacher.id,name,email,teacher.subject_id) 
AND batch(batch.id,venue,batch.teacher_id,date) 
AND takes.subject_id = teacher.subject_id 
AND teacher.id = batch.teacher_id 
AND student_id = takes.student_id 
AND batch_id = batch.id) 

SQL：通过其表REPLACE语句，并通过JOIN或ON或WHERE，对于一些或者出现由SELECT存在，并且在那里想EXISTS：

// student [student_id] takes the subject that is taught by the teacher of batch [batch_id] 
SELECT * 
FROM takes JOIN teacher JOIN batch 
WHERE takes.subject_id = teacher.subject_id 
AND teacher.id = batch.teacher_id 
AND student_id = takes.student_id 
AND batch_id = batch.id 

对于一个约束条件，我们想要一个条件（不是表格），没有满足该条件的行：

// whether THERE EXISTS student_id,batch_id (
    student [student_id] takes the subject that is taught by the teacher of batch [batch_id]) 
EXISTS (...that SELECT...) 

不幸的是，这不是一个约束，你可以很容易地检查在MySQL或大多数DBMS。

编辑：

，并需要得到的信息可以说一批的ID，老师的名字， 学生的某一天的名称。

现在我们正在编写一个查询。我们要行，其中：

FOR batch.id, teacher.name, student.name (
    takes(takes.student_id,takes.subject_id) 
AND teacher(teacher.id,teacher.name,email,teacher.subject_id) 
AND batch(batch.id,venue,batch.teacher_id,date) 
AND student(student.id,student.name,location) 
AND student-batch(student-batch.id,student-batch.student_id,student-batch.batch_id) 
AND takes.subject_id = teacher.subject_id 
AND teacher.id = batch.teacher_id 
AND student.id = takes.student_id 
AND student-batch.student_id = takes.student_id 
AND student-batch.batch_id = batch.id 
AND @date = date) 

这几乎就像除了FOR SOME实际上返回一些列的约束，添加一些其他的线，被点缀些暧昧的名字。 SQL就像直接翻译一样。请注意，现在我们必须加入student-batch，因为约束条件假设我们正在处理来自student-batch的行（id，student_id，batch_id）。

SELECT batch.id AS Batch, teacher.name AS Teacher, student.name AS Student 
FROM takes JOIN teacher JOIN batch JOIN student JOIN student-batch 
WHERE ... AND @date = date 

你可以尝试的ON版本：

SELECT batch.id AS Batch, teacher.name AS Teacher, student.name AS Student 
FROM takes 
JOIN teacher ON takes.subject_id = teacher.subject_id 
JOIN batch ON teacher.id = batch.teacher_id 
JOIN ... 
WHERE @date = date