Thanks you for your good explain of this all - now I have a good idea of how
it works.
Ps. I meant that I'm familiar to simple databases like MS Access etc. but
not of course MySQL witch I think is great! :)
Sumarlidi
-----Original Message-----
From: Carsten H. Pedersen [mailto:[EMAIL PROTECTED]]
Sent: 19. janúar 2001 18:37
To: [EMAIL PROTECTED]; [EMAIL PROTECTED]
Subject: RE: The function of auto_increment and Premier Key?
> Hi I'm relatively new to MySQL though I familiar to other simple
> databases.
Ahem... [takes Sumarlidi aside and explains very carefully how the
MySQL developers feel about hearing MySQL being called a "simple
database" ;-) ]
> I have been reading the manual but not doing well understanding
> the function
> of auto_increment and Premier Key.
>
> Lets say I have a table with a few columns. One of them is an ID with
> auto_increment. It has 1000 rows. If I delete row #500 to #599 (total of
> 100), will the MySQL update the ID value for row #600 to #1000,
No.
> or will it stay as it was?
Yes. The whole point of having such a column is to create and
maintain a unique identifier for the record for as long as it
lives.
> If it stays as it was, and afterwards when I add a row (or
> record), will it
> continue from row #1001 or will it use the value from #500 to #599?
#1001 (same argument -- you don't want something you thought
was dead and gone to seemingly reappearing all of a sudden)
>
> What is the Primary Key used for and how does it work? Do I need it if I
> have a row ID like mentioned above?
In most cases, this is the primary function of the primary key.
The primary key is unique in a couple of respects: 1) it is always
declared as NOT NULL UNIQUE, meaning that you're ensured that
for any record there is always a well-defined, distinct ID as you
must always declare it (or have MySQL do it for you through
auto_increment) and you can never assign the same value to two
different rows; You may have other UNIQUE indexes; however, there
are some subtle differences between these and a primary key.
errrr... hmmmm... I'm sure there are. Though for the life of me,
I can't think of any off the top of my head right now. I'll go
get some coffee while someone else explains this to you.
/ Carsten
--
Carsten H. Pedersen
keeper and maintainer of the bitbybit.dk MySQL FAQ
http://www.bitbybit.dk/mysqlfaq
---------------------------------------------------------------------
Before posting, please check:
http://www.mysql.com/manual.php (the manual)
http://lists.mysql.com/ (the list archive)
To request this thread, e-mail <[EMAIL PROTECTED]>
To unsubscribe, e-mail <[EMAIL PROTECTED]>
Trouble unsubscribing? Try: http://lists.mysql.com/php/unsubscribe.php
