I'll check the site mentioned, thank-you so much!
http://www.artfulsoftware.com/mysqlbook/sampler/mysqled1ch20.html
PB/
-----
/
Ben A. Hilleli wrote:
--------------------
>So you are talking about parent-child relationships in a single table,
or in the technical jargon
>reflexive relationships. See www.artfulsoftware.com
<http://www.artfulsoftware.com/> for detailed examples of how this is
done,
>but here is the thumbnail sketch:
------------------------------
/Actually a Parent-childREN relationship... /
/A USER can have 0 to many friends. /
/This person can also BE THE friend of 0 to many other USERS./
/ /
/AKA: I (A user) can have many friends (other users), I can be the
friend (user) of many users/
--------------------
>The table has to have a ParentID column (call it what you want) that
points, in the case of a
>Friend, to the "Friend Of Whom" UserID column
------------------------------
/Not sure what you mean as aren't you describing a 1 to 1 relation?/
/ /
/I'll check the site mentioned, thank-you so much!/
Ben A. Hilleli
*Programmer / Analyst*
------------------------------------------------------------------------
*From:* Arthur Fuller [mailto:[EMAIL PROTECTED]
*Sent:* October 8, 2008 2:55 PM
*To:* Ben A.H.
*Cc:* mysql@lists.mysql.com
*Subject:* Re: Foreign Keys
So you are talking about parent-child relationships in a single table,
or in the technical jargon reflexive relationships. See
www.artfulsoftware.com <http://www.artfulsoftware.com/> for detailed
examples of how this is done, but here is the thumbnail sketch:
The table has to have a ParentID column (call it what you want) that
points, in the case of a Friend, to the "Friend Of Whom" UserID column.
This simple statement avoids the complexity of the situation where a
Friend can have Friends and so on. That problem requires detailed
explanation, which you can obtain from the site mentioned above. See
also Joe Celko's books.
Arthur
On Wed, Oct 8, 2008 at 3:33 PM, Ben A.H. <[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]>> wrote:
I know that this is the standard means of dealing with a many to many
relationship, I'm just not sure it fits here.
> USER:
> emailID (PK)
> userName
> Password
> Address
> Etc
>
> FRIEND:
> emailID (PK)
>
> USER_FRIEND
> user_emailID (PK)
> friend_emailID (PK)
So if I want a list of USER [EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>'s
friends:
SELECT friend_emailID from USER_FRIEND
WHERE user_emailID="[EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>"
In this (and pretty much every case), the FRIEND table is useless and
doesn't make sense logically.
*I THINK I EXPLAINED THINGS INCORRECTLY*
Let me try again:
* I'm not sure if it's even a true many to many relationship as this is
actually a relationship between ONE RECORD in a TABLE and a ANOTHER RECORD
in THE SAME TABLE!
A USER is:
USER
emailID
userName
A friend is really just another RECORD in the USER table.
i.e. IF I HAD TO MAP THE RELATIONSHIP LOGICALLY, IT WOULD BE:
USER:
emailID
userName
| 1
| many
FRIEND:
emailID
| many
| 1
USER:
emailID
username
(i.e. it's two records in the same USER table)
How are relationships between records in the same table usually dealt with
in terms of design? Implementation?
ThanX,
Ben
""Jim Lyons"" <[EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>>
wrote in message
news:[EMAIL PROTECTED]
> Indexes speed up joins. Foreign keys should be indexes themselves, so
> they
> can also speed up joins. If the FK is not an index, it won't help. So,
> index your FKs
>
> On Wed, Oct 8, 2008 at 10:43 AM, Ben A.H. <[EMAIL PROTECTED]
<mailto:[EMAIL PROTECTED]>> wrote:
>
>> Does using foreign keys simply enforce referential integrity OR can it
>> also
>> speed up JOIN queries?
>>
>>
>>
>> --
>> MySQL General Mailing List
>> For list archives: http://lists.mysql.com/mysql
>> To unsubscribe:
>> http://lists.mysql.com/[EMAIL PROTECTED]
>>
>>
>
>
> --
> Jim Lyons
> Web developer / Database administrator
> http://www.weblyons.com <http://www.weblyons.com/>
>
--
MySQL General Mailing List
For list archives: http://lists.mysql.com/mysql
To unsubscribe:
http://lists.mysql.com/[EMAIL PROTECTED]
------------------------------------------------------------------------
No virus found in this incoming message.
Checked by AVG - http://www.avg.com
Version: 8.0.173 / Virus Database: 270.7.6/1713 - Release Date: 10/7/2008 6:40 PM
