References to Cardinality in index tables - what is meant by this?

[MLH]

Cardinality?

I hear it spoken of by MySQL users. Does it
matter to MS Access if MySQL tables are
attached via ODBC?

[Larry Linson]

"MLH" <CR**@NorthStat e.net> wrote in message
news:7b******** *************** *********@4ax.c om...

Cardinality?

I hear it spoken of by MySQL users. Does it
matter to MS Access if MySQL tables are
attached via ODBC?

As far as I know, MyODBC is the _only_ way to access MySQL tables from
Access. Perhaps there is an ADODB data provider, but I haven't heard about
it.

[MLH]

Thanks, Larry. Long time, no talk to. How have you been?
My question was vague. Allow me to rephrase. I was wondering
about cardinality in MySQL tables, and what significance it
might have to me and my MS Access application housing
the attached tables.

xxxxxxxxxxxxxxx xxxxxxxxxxxxxxx xxxxxxxxxxxxx
On Tue, 07 Sep 2004 02:29:20 GMT, "Larry Linson"
<bo*****@localh ost.not> wrote:

"MLH" <CR**@NorthStat e.net> wrote in message
news:7b******* *************** **********@4ax. com...

Cardinality?

I hear it spoken of by MySQL users. Does it
matter to MS Access if MySQL tables are
attached via ODBC?

As far as I know, MyODBC is the _only_ way to access MySQL tables from
Access. Perhaps there is an ADODB data provider, but I haven't heard about
it.

[Tony Toews]

MLH <CR**@NorthStat e.net> wrote:

Cardinality?

I hear it spoken of by MySQL users. Does it
matter to MS Access if MySQL tables are
attached via ODBC?

Seems to me this is two questions.

From point 8 on http://www.sqlteam.com/item.asp?ItemID=122

"Cardinalit y helps us further understand the nature of the relationship between the
child entity and the parent entity. The cardinality of a relationship may be
determined by asking the following question: "How many instances of the child entity
relate to each instance of the parent entity?". There are four types of cardinality:
(1.) One to zero or more (common cardinality), (2.) One to one or more (P
cardinality), (3.) One to zero or one (Z cardinality), and (4.) One to exactly N (N
cardinality)."

I'd have trouble thinking of any situations where it was anything but #1. Well, ok
#2 a lot of time times as most often you are going to have child records. But #1
will exist for a few moments in time until you add the child record.

There's nothing like this in Access. I don't know for sure about SQL Server but I
doubt it. And given that case 2 is a subset of 1 and 3 or 4 are so rare it's not
worth having this specified in the database engine.

Now to me if MySQL supports this specification on the join and you break it you are
going to get some kind of error reported back to Access. Whatever and however that
works. I'd say try it and see what happens.

Tony
--
Tony Toews, Microsoft Access MVP
Please respond only in the newsgroups so that others can
read the entire thread of messages.
Microsoft Access Links, Hints, Tips & Accounting Systems at
http://www.granite.ab.ca/accsmstr.htm

[Larry Linson]

"MLH" wrote

Thanks, Larry. Long time, no talk to. How have you been?
Still hangin' in there.
My question was vague. Allow me to rephrase. I was wondering
about cardinality in MySQL tables, and what significance it
might have to me and my MS Access application housing
the attached tables.

I answered the part that I knew something about, which was connecting via
ODBC. <G>

Tony has covered the definition of cardinality very well. I've never seen it
raised as an issue in any newsgroup article about Access and MySQL, nor in
the documentation about MySQL that I downloaded.

Larry Linson
Microsoft Access MVP

[MLH]

Thanks. I'll have to digest it all.
xxxxxxxxxxxxxxx xxxxxxxxxxxxxxx xxxxxxxx

On Tue, 07 Sep 2004 22:02:52 GMT, Tony Toews <tt****@teluspl anet.net>
wrote:

MLH <CR**@NorthStat e.net> wrote:

Cardinality ?

I hear it spoken of by MySQL users. Does it
matter to MS Access if MySQL tables are
attached via ODBC?

Seems to me this is two questions.

From point 8 on http://www.sqlteam.com/item.asp?ItemID=122

"Cardinalit y helps us further understand the nature of the relationship between the
child entity and the parent entity. The cardinality of a relationship may be
determined by asking the following question: "How many instances of the child entity
relate to each instance of the parent entity?". There are four types of cardinality:
(1.) One to zero or more (common cardinality), (2.) One to one or more (P
cardinality) , (3.) One to zero or one (Z cardinality), and (4.) One to exactly N (N
cardinality) ."

I'd have trouble thinking of any situations where it was anything but #1. Well, ok
#2 a lot of time times as most often you are going to have child records. But #1
will exist for a few moments in time until you add the child record.

There's nothing like this in Access. I don't know for sure about SQL Server but I
doubt it. And given that case 2 is a subset of 1 and 3 or 4 are so rare it's not
worth having this specified in the database engine.

Now to me if MySQL supports this specification on the join and you break it you are
going to get some kind of error reported back to Access. Whatever and however that
works. I'd say try it and see what happens.

Tony