Re: Tables and foreign keys

On Dec 26, 2011, at 1:57 AM, Amit Tandon wrote:

> Dear Karl
>
> Foreign key is a good option (provided you use InnoDB database) to  
> automate
> the deletion/updation of cart details when you remove cart.
>
> Besides 1:1 cardinality is good or bad can only be decided on the  
> semantics
> of your tables.
>
> As a an aside, if it is 1:1 cardinality, then you can probably merge  
> the
> two tables
> ============
> regds
> amit
>
> "The difference between fiction and reality? Fiction has to make  
> sense."
>
>
> On Mon, Dec 26, 2011 at 12:38 PM, Karl DeSaulniers <[email protected] 
> >wrote:
>
>> Hello all,
>> I have two database tables. Cart and a cartdetails.
>> I want the information for the cartdetails to be based on/ 
>> autofilled info
>> from cart.
>> I want the ability to delete from cart and cartdetails to  
>> automatically
>> clear as well.
>> Would a foreign key be best suited for this? What kind of cardnaility
>> would I use 1:1 ?
>> Hope I make sense.
>>
>> Hope everyone had a great holidays!
>>
>> Best,
>>
>> Karl DeSaulniers
>> Design Drumm
>> http://designdrumm.com
>>
>>


Thanks Amit for the reply.
Ok, so if you can not merge the two tables, then it is not a 1:1  
relationship?

EG:

(table)CART:
	cartID - PRIMARY
	username
	firstname
	lastname
	product
	long description
	quantity
	options
	price

(table)CARTDETAILS:
	cartdetailsID
	cartID - Foreign Key (Unique)
	product
	short description (taken from long des. in CART)
	quantity
	options
	price

Is this a 1:1 if the key is between the two cartID's?
What is actually happening when I make a foreign key?
What does the foreign key cover? Just the row its linked to or the  
whole table?

For this structure I would like, in order for their to be cartdetails,  
there should be a cart.
If there is a cart then a cartdetails needs to automatically/ 
progmatically generate.
(I think I read somewhere that MySQL is capable of doing this before  
sending back responses. Please correct me if I am wrong or if its  
unrelated.)

What kind of relation is that?
Also, if you or someone could explain what these cardinality rules  
mean. What..

0 or 1  does?
1+       does?
0,1+    does?
Many (kind-of figured this one out, perhaps not.)
etc..

I think that would help me greatly. I hope I am not sounding like a  
help vamp.
I only ask because my google foo has failed me on where to search for  
these specific answers.
Links are appreciated. I like to do stuff on my own but sometimes the  
brain cramps. :)
TIA

Best,

Karl DeSaulniers
Design Drumm
http://designdrumm.com