Re: Tables and foreign keys

On Dec 26, 2011, at 3:05 AM, Amit Tandon wrote:

> ============
> regds
> amit
>
> "The difference between fiction and reality? Fiction has to make  
> sense."
>
>
> On Mon, Dec 26, 2011 at 1:55 PM, Karl DeSaulniers <[email protected] 
> >wrote:
>
>> 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?
>>
> No! it is 1:N becuase of Multiple rows in Cartid = 1 row in Cart
>
>
>> What is actually happening when I make a foreign key?
>>
> You link the two tables and try to find matching rows of cart in  
> cart id
>
>> What does the foreign key cover? Just the row its linked to or the  
>> whole
>> table?
>>
> The foreing key helps you uniquely identift set of rows. Foerign key
> actully help you identify the row(s). And then column of thos rows  
> give you
> your value
>
>> 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?
>>
> 1:1
>
>> 1+       does?
>>
> 1:M
>
>> 0,1+    does?
>>
> M:N - you figure correctly. But this is for both the tables i.e 1+
> psosibility in both the tables. And this is generally table which is  
> linked
> to two tables

So the 0=first table and ,1+ = subsezuent tables?
Is there such thing as 1+,0? Or is that what 1+ is?
Sry, the coma throws me off a bit.

>
>> 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
>>
>>


Thanks..
I think that got the knot out a little.. :)

Best,

Karl DeSaulniers
Design Drumm
http://designdrumm.com


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