Thank you!
On Dec 26, 2011, at 4:12 AM, Amit Tandon wrote:
Dear Karl
Refer Wiki entry. 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
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Karl DeSaulniers
Design Drumm
http://designdrumm.com
