Dear KarlRefer Wiki entry<http://en.wikipedia.org/wiki/Entity-relationship_model>. The last diagram shows one to many relationship in many ways. That may help you in clearing your doubts about the comma which is a way of representing the relationship Quoted from MS Access example One-To-Many Relationships A one-to-many relationship is the most common type of relationship. In this type of relationship, a row in table A can have many matching rows in table B, but a row in table B can have only one matching row in table A. For example, the Publishers and Titles tables have a one-to-many relationship: each publisher produces many titles, but each title comes from only one publisher. A one-to-many relationship is created if only one of the related columns is a primary key or has a unique constraint. Many-To-Many Relationships In a many-to-many relationship, a row in table A can have many matching rows in table B, and vice versa. You create such a relationship by defining a third table, called a junction table, whose primary key consists of the foreign keys from both table A and table B. For example, the Authors table and the Titles table have a many-to-many relationship that is defined by a one-to-many relationship from each of these tables to the TitleAuthors table. The primary key of the TitleAuthors table is the combination of the au_id column (the authors table’s primary key) and the title_id column (the Titles table’s primary key). One-To-One Relationships In a one-to-one relationship, a row in table A can have no more than one matching row in table B, and vice versa. A one-to-one relationship is created if both of the related columns are primary keys or have unique constraints. ============ regds amit "The difference between fiction and reality? Fiction has to make sense." On Mon, Dec 26, 2011 at 2:43 PM, Karl DeSaulniers <karl@xxxxxxxxxxxxxxx>wrote: > > 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 <karl@xxxxxxxxxxxxxxx >> >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@xxxxxxxxxxxxxxx >>>> >>>>> 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 > > > -- > PHP Database Mailing List (http://www.php.net/) > To unsubscribe, visit: http://www.php.net/unsub.php > >
