Re: Tables and foreign keys

============ regds amit "The difference between fiction and reality? Fiction has to make sense." On Mon, Dec 26, 2011 at 1:55 PM, Karl DeSaulniers <karl@designdrumm.com>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 <karl@designdrumm.com >> >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 > 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 > >