The manual also states that INDEX is a synonym for KEY, which means that
they have identical funcationality.
Daniel Åkerud
----- Original Message -----
From: "Cal Evans" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>; "Marco Bleeker" <[EMAIL PROTECTED]>
Sent: Friday, June 22, 2001 6:27 PM
Subject: Re: KEY and index
> KEY is used to build other indexes. It's not short for Primary Key.
There
> are PRIMARY KEY indexes, candidate key indexes (these COULD be a primary
key
> but for one reason or another , are not) and just regular indexes.
>
> All tables should have a primary key. (I'm partial to adding an
> auto_increment field to almost every table of the name <tableName>ID and
> making this my primary key) Some tables will also have a candidate key.
This
> is especially true if you manufacture a PK like I do. Then there may be a
> piece of data that is unique to each record and never null that would
> normally serve as a primary key. (The reason I manufacture PKs is because
if
> a piece of data means something then it is always possible that it will
> change.This means that you would have to trace down all your FK
> relationships and change the data in those tables as well.SSN, phone
number,
> email address are all examples of candidate keys but also smart keys. I
> never use them as PKs. )
>
> Regular keys are just indexes, not necessarily unique, not necessarily on
> fields that don't accept nulls. Their primary function is to speed up data
> retrieval. Use them sparingly as they can have a negative impact on
> inserting and updating records.
>
> HTH,
> Cal
> *
> * Cal Evans
> * Senior Internet Dreamer
> * http://www.calevans.com
> *
> ----- Original Message -----
> From: "Marco Bleeker" <[EMAIL PROTECTED]>
> To: <[EMAIL PROTECTED]>
> Sent: Friday, June 22, 2001 9:36 AM
> Subject: KEY and index
>
>
> > Hello, I am learning MySQL and have a question. I know about the
> importance
> > of the PRIMARY KEY statement, but I also see a KEY statement being used
> > when creating a table. Is this just short for PRIMARY KEY, or what's the
> > difference?
> >
> > Second question, when I have a large table, but with only 2 small cells
> per
> > row (2 columns), is it useful to create a PRIMARY KEY, KEY, or INDEX for
> > speed (there is no set relation to another table).
> >
> > Third question, when exactly does MySQL use indexes. Is it used when the
> > indexed column is part of a (SELECT *) WHERE statement, together with a
> > non-indexed column? I just want to check if matching a row is present or
> > not, not actually retrieve information ("WHERE ip='$ip' and
> date>curdate()")
> >
> > Thanks, Marco
> > |
> > | Marco Bleeker, Amsterdam
> > | [EMAIL PROTECTED]
> > | http://www.euronet.nl/users/mbleeker/
> > |
> > | Attachments only after prior notice please.
> > | Don't put me on any kind of mailing list.
> > |
> > | I am now receiving the Snowhite virus 4x a day
> > | - some of you must be infected, please check !
> > | (No, you did not get it from me, I use Eudora)
> > | __@
> > | _`\<,_
> > |__(*)/ (*)________________Ah, op DIE fiets !
> >
> >
> >
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