将数据库规范化为3NF [英] Normalizing a Database up to 3NF

问题描述

规范化数据库; orignally它conatin列如姓名，Phoneno，EmailAddress，地址，技能



因为每个学生可能有更多技能。



1 NF：







Studentid（PK）FirstName LastName Phoneno EmailAddress StreetName City

1 F1 L1 88889 [e-mail] westend pune

2 F2 L2 8888 [e-mail] Eastend Mumbai



skillid（PK）skillname studentid（FK）

1 Java 1

2 .Net 2

3 Android 1

4甲骨文1



你可以指导我应该是我的2NF和3NF正常形式：

将技能（PK）需要删除所以数据库是否在2NF？

每次我去采访时我都没能写数据库规范化到3NF

normalizing Database; orignally it conatin column like Name,Phoneno,EmailAddress,Address , skill

As each student may have more skill.

1 NF:



Studentid(PK) FirstName LastName Phoneno EmailAddress StreetName City
1 F1 L1 88889 [e-mail] westend pune
2 F2 L2 8888 [e-mail] Eastend Mumbai

skillid(PK) skillname studentid(FK)
1 Java 1
2 .Net 2
3 Android 1
4 Oracle 1

Can u guide me what should be my 2NF & 3NF Normal form:
will skillid(PK) need to remove so database to be in 2NF?
Each time as i go to interview & i failed to write databse normalization upto 3NF

推荐答案

此处 [ ^ ]是一个列表。如果我在采访中得到了很多，我会记住表格（实际上，我是这样做的），然后问他们你的意思是标准还是博伊斯 - 科德的正常形式？我打赌有一半人问你，不知道这意味着什么。



要达到第二范围，你要删除适用于表格多行的数据子集并将它们放在单独的表格中。



要获得第三范式，请删除与主键无关的任何列。



第二次正常：



从第二张表中删​​除技能ID。创建一个连接表，如果两个学生具有相同的技能，则技能在表格中一次，并在加入表中加入两次。



您的数据意味着更多一个学生可以拥有相同的电子邮件。如果这是真的，那么我想这需要考虑因素，但他们肯定更有可能拥有相同的地址或电话号码，因此它成为一个问题，你想要多么精细。



我在这里看不到任何直接违反第三范式的内容，这是我怀疑你的面试官知道他们想要你的想法的原因之一。

Here[^] is a list. If I was getting this in interviews a lot, I would both memorise the forms ( actually, I did that any how ), and ask them 'do you mean standard or Boyce-Codd normal form' ? I bet half the people asking you, won't know what that means.

To get to second normal you remove subsets of data that apply to multiple rows of a table and place them in separate tables.

To get to third normal form you remove any columns that are not related to the primary key.

Second normal:

remove the skill id from the second table. Create a joining table so if two students have the same skill, the skill is in table a once, and joined to twice in the joining table.

Your data implies more than one student can have the same email. If this is true, then I guess that would need to be factored out, but they are surely more likely to have the same address or phone number, so it becomes a question of how granular you want to be.

I don't see anything here that directly violates the third normal form, which is one reason that I doubt your interviewers know as much as they want you to think.

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