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 <karl@designdrumm.comwrote:

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