i have a table Students which contains the following colums:
Id,FirstName,LastName,Adress.
The colum Adress will contain just the street adress.
the question is: will it be better for the database optimization to isolate the column Adress in a different table?
Yes. If you seperate it into another table, you can have more than one address per person. If you seperate it to two different tables, an Address table and a StudentAddress table to map the two together, you can make sure that a single address is shared between people or even track a history of addresses for one person. Further, in a seperate table you can break the address down into columns so that you can easily search by City or Province or Country.
You can't do any of that putting an Address into a single column with the Student table.
It depends on how you are going to treat that Address. If you will need to treat it as different entity, i.e. link single address to several Students or vice versa e.t.c., then you should do normalization.
If address is only attribute of entity student then leave it as is.
For full proper data structures to manage addresses: THe Data Model Ressource BOok, Volume 1. It is a LOT more complicate to get right than you think.
Related
I am designing a database for a system and I came up with the following three tables
My problem is that an Address can belong to either a Person or a Company (or other things in the future) So how do I model this?
I discarded putting the address information in both tables (Person
and Company) because of it would be repeated
I thought of adding two columns (PersonId and CompanyId) to the
Address table and keep one of them null, but then I will need to add
one column for every future relation like this that appears (for
example an asset can have an address where its located at)
The last option that occur to me was to create two columns, one
called Type and other Id, so a pair of values would represent a
single record in the target table, for example: Type=Person,Id=5 and
Type=Company,Id=9 this way I can Join the right table using the type
and it will only be two columns no matter how many tables relate to
this table. But I cannot have constraints which reduce data integrity
I don't know if I am designing this properly. I think this should be a common issue (I've faced it at least three times during this small design in objects like Contact information, etc...) But I could not find many information or examples that would resemble mine.
Thanks for any guidance that you can give me
There are several basic approaches you could take, depending on how much you want to future proof your system.
In general, Has-One relationships are modeled by a foreign key on the owning entity, pointing to the primary key on the owned entity. So you would have an AddressId on both Company and Person,which would be a foreign key to Address.Id. The complexity in your case is how to handle the fact that a person can have multiple addresses. If you are 100% sure that there will only ever be a home and work address, you could put two foreign key columns on Person, but this becomes a big problem if there's a third, fourth, fifth etc. address. The other option is to create a join table, PersonAddress, with three columns a PersonId an AddressId and a AddressType, to indicate whether its a home work or whatever address.
I have following two entities, where a person address is kept in a separate table because a person can have multiple addresses.
The mailing address however is one of the multiple addresses stored in address table, which is to be referred in person table.
Can following relationship exist?
The answer to your direct question is "Yes". However, you cannot declare the model only using create table because:
Declaring the foreign key address.person_id requires that the person table already exist.
Declaring the foreign key person.mailing_address requires that the address table already exist.
Hence, to implement the model, you need to use alter table to add one or both of the constraints after both tables are created.
Is this the model you want? One feature of an address is that multiple people can have the same address. Your model does not allow that. To handle this, you would typically have three tables:
Person
Address
PersonAddress
The third table has one row for each person/address pair. It can also have other information such as:
Type ("mailing" versus other types)
Effective and end dates.
Perhaps other information.
If you want to guarantee uniqueness of the "mailing" address in such a model, many databases support filtered unique indexes, to ensure there are no duplicate mailing addresses.
I'm not sure why you have person_id as an fk on address but that doesn't look correct. There are lots of correct ways to model this and the best one for you will depend on you particular circumstances - but a couple of options are:
If you know all the types of addresses there can be then add multiple address fk fields to the person e.g. billing address, shipping address, etc. This makes querying quick and simple but is inflexible: adding a new address type in the future is relatively complex to implement
Add an intersection table with fks for person and address and an address type field. This has a slight overhead when it comes to querying but has the advantage if being very flexible: adding a new address type is trivial
[Assuming there is a one to many relationship between an individual and an address, and assuming there is a one to many relationship between an agency and an address.]
Given the following table structure:
Wouldn't you want to merge the two address tables together and instead of using a foreign key within each one use a tie table?
Like this:
Are they both valid for normalization or only one?
Depends what you want to do.
In your second example with the tie tables, if I want to do a mailshot to my customers then my query has to go out to the agency tie table to exclude any agency addresses.
Of course you could have an address type column to differentiate but then you have a more complex query for your insert statement.
So although "address" is a global idea, sometimes it is easier to have it segregated by context.
Secondly, your customer data would usually be changing much more than your agency data. There may also be organisational and legal requirements around storage of personal data that make it better to separate the two.
e.g. in a health records system I want to be able to easily extract / restrict client data and to keep my configuration or commissioning data separate.
Thus in all the client systems I have used, the model tends to be the first one you describe rather than the second.
For my app I have Cinemas and Addresses. Cinemas are related to Addresses through a foreign keys. When displaying a list of Cinemas I want to filter them by Addresses.Districts.name of the Cinema.
how can i make such a query in Dreamfactory API?
This should give you a little more of an idea on how to approach your query, though your data model may be slightly more complex than this...
Here is a simple example:
Let's assume Cinemas is the parent table and Addresses is the child
table.
Each Cinema can have any number of related Addresses.
The Addresses table has a column named "CinemaId".
To get all Cinemas that have an Address where state=CA you could make
the following query.
GET /rest/db/Addresses?related=Cinemas_by_CinemaId&filter=state='CA'
It's a good idea to escape filter string to state%3D'CA'.
In the results each Addresses record that matched the query will
contain the parent Cinemas record as an object named
Cinemas_by_CinemaId.
Let us know if you need a little more insight.
Suppose i have a table with 3 fields
Person_id, Name and address. Now the problem is that a person can have multiple addresses. and the principle of atomic values says that data should be atomic.
So then how am i suppose to store multiple addresses for a single person ?
You're supposed to create an ADDRESS table that has a foreign key linking it to a PERSON record, i.e. PERSON_ID. This is the "relational" component of a relational database, and it's why it's more flexible than a flat file (which is like a single table).
Put adresses in a second table, give each adress a "Person ID", so that mutiple rows in the adress-table can referr to on person.
I would suggest adding a address type to the address table to identify which type of address it is (Home, Vacation, Office), etc. Something like: AddType that refers to a list table where more types could be added down the road.