-------------------- >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]> 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]'s friends: SELECT friend_emailID from USER_FRIEND WHERE user_emailID="[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]> 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]> 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]
