Hank,

Thanks, that was precisely the information I was hoping to get.  I've been
looking at the MySQL online manual and it lists everything but does go into
specifics on the actual implementation of some things.  It "may" do so, but
is not readily apparent to me if it does.

One more question, for you or anyone.  I have inserted over 17,000 rows into
the table I just created.  Each row has 8 columns (the table list all makes,
models, and types of cars since 1980 and tells what their tire size and
front and rear recommended tire pressure is).

I can construct basic queries and results,etc. but how do I do this -  How
do I build an array (I assume this is what I need) or a query that will look
for, and grab, only one occurence of an item if it occurs multiple times?
For instance, I want to list all of the available makes of cars.  I may have
300 Buicks (different models, but not a concern at this point) and 240
Hondas.  I want to be able to allow the user to select from, in this case, a
Honda or a Buick. My goal here is to create a series of screens that will
allow the user to drill down to their car type without actually typing in
information (since some of the options for these vehicles are multi-word and
I want to have tight control over the returned items).

Eventually the user will be shown a screen that will echo the values of the
following fields for one specific car (one row of the database table):

year, make, model, option, tire_pressure, front_pz, rear_pz (the actual
names of the columns)

Thanks,
Keith D Sellars
WebGraffix
www.webgraffix.com

"Making database sites seem easy"

----- Original Message -----
From: "Hank Marquardt" <hmarq(at)yerpso.net>
To: "Keith Sellars" <Keith(at)webgraffix.com>
Cc: <hwg-languages(at)hwg.org>
Sent: Monday, September 23, 2002 3:34 PM
Subject: Re: mysql field types


> On Mon, Sep 23, 2002 at 03:05:29PM -0400, Keith Sellars wrote:
> > I'm teaching myself more and more about php and mysql as time permits.
I've
> > in the process of setting up a new table on an existing mysql database.
I
> > have a few questions:
> >
> > When should I use "varChar" instead of, say, "text" or "blob"?
>
> Space, indexing and storage effiency are the things you're balancing
> here -- not to mention, 'the right tool for the job'
>
> char v. varchar -- if you have a known length text string, use char (2
> char state codes, 32 byte digital signatures).  I you have varying
> character length to some determined maximum which is shorter than the
> type can hold varchar is your friend.  Names, addresses, short text
> fields ...
>
> text is an unlimited version of varchar from the standpoint of
> implementation -- the difference is that the entry itself is stored
> separately from the record and different indexing routines must be used.
> It is space efficient, but query inefficient.
>
> blob = "binary large object" -- most commonly used for storing pictures
> in practice, though any binary data is appropriate.  blobs are evil (my
> thought) ... they are implentation specific and require special
> retrieval/display code; conversions between db engines are messy ...
> they have their place; but you need to know when and when not to use
> them.
>
> >
> > When should I use "int" instead of "tinyInt" or vice versa?
> >
>
> Just use int and be happy:) ... generally the only time you'll violate
> this is if you *know* you need to and then it'll usually be on the high
> end that you violate (where you need a value greater than a normal
> integer can hold)
>
> > What are the advantages in the cases above of one or the other, or
> > advantages for other similar field types?
> >
>
> Speed, storage efficiency and indexing are the things you're balancing
> ... for small datasets, you can usually ignore these considerations and
> just use what's comfortable.  As dataset size grows you need to worry
> more particularly about indexing
>
> > When should I make a field "not null" or "null"?  How important is this
to
> > be set either way?
> >
>
> Data integrity -- the more general issue is how to use constraints
> within the database -- mysql is pretty weak in this area; go look at the
> manual for postgresql and you'll see what can be done in this area.  In
> specific null vs. not null is saying "Must this field have data?" ... if
> the answer is yes, then you'll "not null" is the answer --*AND*-- if you
> try to insert a record with that field unset, it will trigger a database
> error and the insert will fail.
>
> > Thanks,
> > Keith D Sellars
> > WebGraffix
> > www.webgraffix.com
> >
> > "Making database sites seem easy"
> >
>
> --
> Hank Marquardt <hank(at)yerpso.net>
> http://web.yerpso.net
> GPG Id: 2BB5E60C
> Fingerprint: D807 61BC FD18 370A AC1D  3EDF 2BF9 8A2D 2BB5 E60C
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>

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