在ERD中获得主键和外键 [英] To get primary and foreign keys right in ERD
问题描述
我阅读了我的笔记,我现在不确定这些键。
I read my notes and I am now unsure about the keys.
我的逻辑图
alt text http://files.getdropbox。 com / u / 175564 / db / db-11.png
此表格应符合以下实体ERD
This table should be in line with the following physical ERD
alt text http:// files。 getdropbox.com/u/175564/db/db-22.png
我在表格中只有一个外键问题
I have only one foreign key in the table Question
.
我想知道
- 应该在表中 Question-tag-xref 中的
question-id
和问题标记
, / li>
- should the
question-id
andquestion-tag
in the table Question-tag-xref, ANDquestion-id
andanswer
in the table Answers be also foreign keys?
推荐答案
Masi - 逻辑模型通常不包含数据类型(string,int等)信息,但是指示属性(成为物理模型中的列)是否是可选的(可以为空或不为空)。
Masi - Logical models don't usually contain data type (string, int, etc) information, but do indicate if the attribute (becomes a column in the Physical model) is optional (able to be null or not).
-ID和QUESTION-TAG列将是QUESTION-TAG-XREF表中的外键。以下是QUESTION-TAG-XREF的物理视图:
That said, yes - the QUESTION-ID and QUESTION-TAG columns would be foreign keys in the QUESTION-TAG-XREF table. Here's a physical view of QUESTION-TAG-XREF:
QUESTION-TAGS-XREF
- QUESTION-ID(与QUESTIONS表格的pk,fk关系)
- QUESTION-TAG-CODE(pk,fk与QUESTION-TAG表格的关系)
这两列都是pk,以确保您不能对给定问题出现重复的标签。
Both columns are the pk to ensure you can't have duplicate tags for a given question.
您提供的QUESTION表中的QUESTION-ID是否为ANSWERS表中的外键是正确的。
You are correct that QUESTION-ID would be a foreign key in the ANSWERS table, in reference to the QUESTION table.
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