So you are talking about parent-child relationships in a single table, or in the technical jargon reflexive relationships. See 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 > > > > > > -- > MySQL General Mailing List > For list archives: http://lists.mysql.com/mysql > To unsubscribe: > http://lists.mysql.com/[EMAIL PROTECTED] > >
