在Jxn Tbl中分开PK？ [英] Separate PK in Jxn Tbl?
问题描述
每当我在过去创建过联结表时，我总是将联合表的PK与
的PK结合在另外两个表中。例：表1
PK = A;表2 PK = B;连接表由两个字段A和B组成，其中
一起构成了连接表的PK。
但是，我刚刚遇到了一些代码该人创建了一个交叉点
表，其中包含一个由自动编号字段组成的单独PK，然后是两个
字段。
所以我想知道其他人如何做联结表 - 用一个独立的
自动编号PK，或者用表格的PK组成的PK是什么？b $ b加入？并且，如果是独立PK，那么为什么？
谢谢！
Neil
Whenever I''ve created junction tables in the past, I always made the PK of
the junction table the combined pks from the two other tables. Ex: Table1
PK=A; Table2 PK=B; Junction table consists of two fields, A and B, which
together comprise the PK for the junction table.
However, I just came across some code in which the person created a junction
table with a separate PK consisting of an autonumber field, and then the two
fields.
So I was wondering how others did junction tables -- with a standalone
autonumber PK, or with a PK consisting of the PKs of the tables being
joined? And, if a standalone PK, then why?
Thanks!
Neil
推荐答案
我总是只使用2个主键，但....
如果我是一个图书馆，将1本书的2个无法复制的副本借给同一个
人，我想我需要一个Autonumber PK加一个BookID和
BorrowerID。
Phil
尼尔 < no **** @ nospam.netwrote in message
news：6k *************** @ newssvr14.news.prodigy.net。 ..
I always use just the 2 primary keys but....
If I were a library lending 2 undiffentiatable copies of 1 book to the same
person, I suppose I would need an Autonumber PK plus A BookID and
BorrowerID.
Phil
"Neil" <no****@nospam.netwrote in message
news:6k***************@newssvr14.news.prodigy.net. ..
每当我在过去创建过联结表时，我总是把联合表的PK作为结合表的PK来自另外两张桌子。例：表1
PK = A;表2 PK = B;连接表由两个字段A和B组成，其中
一起构成了连接表的PK。
但是，我刚刚遇到了一些代码该人创建了一个
联结表，其中包含一个由自动编号字段组成的单独PK，然后是两个字段的
。
所以我想知道其他人如何做联结表 - 用一个独立的
自动编号PK，或者用表格的PK组成的PK是什么？b $ b加入？而且，如果是独立PK，那么为什么呢？
谢谢！
Neil
Whenever I''ve created junction tables in the past, I always made the PK of
the junction table the combined pks from the two other tables. Ex: Table1
PK=A; Table2 PK=B; Junction table consists of two fields, A and B, which
together comprise the PK for the junction table.
However, I just came across some code in which the person created a
junction table with a separate PK consisting of an autonumber field, and
then the two fields.
So I was wondering how others did junction tables -- with a standalone
autonumber PK, or with a PK consisting of the PKs of the tables being
joined? And, if a standalone PK, then why?
Thanks!
Neil
" Neil" < no **** @ nospam.netwrote in message
news：6k *************** @ newssvr14.news.prodigy.net。 ..
"Neil" <no****@nospam.netwrote in message
news:6k***************@newssvr14.news.prodigy.net. ..
所以我想知道其他人如何使用独立的
自动编号PK，或者使用由表格的PK是否已加入？b $ b？而且，如果是独立PK，为什么呢？
So I was wondering how others did junction tables -- with a standalone
autonumber PK, or with a PK consisting of the PKs of the tables being
joined? And, if a standalone PK, then why?
PK由FK组成，引用正在连接的表格。
这是你的意思吗？ />
With a PK consisting of the FKs that reference the tables being joined.
Is that what you meant?
2008年1月22日星期二20:26:42 GMT，Neil < no **** @ nospam.netwrote：
On Tue, 22 Jan 2008 20:26:42 GMT, "Neil" <no****@nospam.netwrote:
>所以我想知道别人怎么做联结表 - 用独立的
自动编号PK ，或者由表格的PK组成的PK加入？而且，如果是独立PK，为什么呢？
>So I was wondering how others did junction tables -- with a standalone
autonumber PK, or with a PK consisting of the PKs of the tables being
joined? And, if a standalone PK, then why?
我做过两件事;单独的主键是（严格来说）永远不需要
，但如果联结表本身是相关的，它可以很方便
一对多的附加表或表。访问不会使多字段
所有易于使用的外键（例如，你不能在组合框中使用它们没有一些杂乱的代码而无需使用它们。） />
如果我这样做，我将始终在两个
父外键字段上指定唯一（非主要）索引。
John W. Vinson [MVP]
I''ve done both; the separate primary key is (strictly speaking) never
necessary, but it can be handy if the junction table is itself related
one-to-many to an additional table or tables. Access doesn''t make multifield
foreign keys all that easy to use (e.g. you can''t use them in a combobox
without some messy code).
If I do so, I will always specify a unique (non-primary) Index on the two
parent foreign key fields.
John W. Vinson [MVP]
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