This question may answer itself, but it is also a question of best practices.
I am designing an application that allows users (comapnies) to create an account. Those users are placed in a table "Shop_table". Now each shop has dynamic data, however the tables would be the same for each shop, like shop_employees, shop_info, shop_data.
Would it be more effective to have a specific table for each shop or would I just link their data by the shop id.
For example:
shop: Dunkins with id:1
shop: Starbucks with id:2
would dunkins have its own dunkins_shop_employees, dunkins_shop_info, dunkins_shop_data tables
and Starbucks have its own starbucks_shop_employees , starbucks_shop_info , starbucks_shop_data
or would i have one table shope_employees, shop_info, shop_data and link by id 1 or 2, etc..
Definitely one table for each entity with a field to identify the company.
If all the companies have the same information there is no need to create tables for each, and if you did your queries will become a nightmare.
Do you really want a load of UNION queries in order to get any aggregate data across companies? You will also have to modify all queries in your DB as soon as another company (and therefore multiple tables) are added.
Define your tables independently, model the entities you want to store and dont think about who they belong to.
You should have only one table ( for each shop_info etc.. )
Creating similar tables is a maintenance nightmare. You will need to create similar foreign keys, similar constraints, similar indexes, etc.
If your concern is privacy, this should be controlled in your application. You application should always add a "WHERE" clause based on who is logged in/ querying.
If you absolutely need to - you can create views which where clause as shop_id. You can give rights to various people on the view only. This would only make sense if you had a big customer who wanted some SQL level query ability.
Related
Recently I encountered an application, Where a Master Table is maintained which contain the data of more than 20 categories. For e.g. it has some categories named as Country,State and City.
So my question is, it is better to move out this category as a separate table and fetching out the data through joins or Everything should be inside a single table.
P.S. In future categories count might increase to 50+ or more than it.
P.S. application based on EF6 + Sql Server.
Edited Version
I just want to know that in above scenario what should be the best approach, one should go with single table with proper indexing or go by the DB normalization approach, putting each category into a separate Table and maintaning relationship through fk's.
Normally, categories are put into separate tables. This conforms more closely with normalized database structures and the definition of entities. In particular, it allows for proper foreign key relationships to be defined. That is a big win for data integrity.
Sometimes categories are put into a single table. This can, of course, be confusing; consider, for instance, "Florida, Massachusetts" or "Washington, Iowa" (these are real places).
Putting categories in one table has one major advantage: all the text is in a single location. That can be very handy for internationalization efforts. To be honest, that is the situation where I have seen this used.
We have a situation in a database design in our company. We are trying to figure out the best way to design the database to store transactional data. I need expert’s advice on the best relational design to achieve it. Problem: We have different kind of “Entities” in our system, for example; Customers, Services, Dealers etc. These Entities are doing transfer of funds between each other. We need to store the history of the transfers in database.
Solutions:
One table of transfers and another table to keep “Accounts” information. There are three tables “Customers”, “Services”, “Dealers”. There is another table “Accounts”. An account can be related to any of the “Entities” mentioned above; it means (and that’s the requirement) that logically there should be a one-to-one relationship to/from Entities and Accounts. However, we can only store the Account_ID in the Entities table, but we cannot store the foreign key of Entities in Accounts table. Here the problem happens in terms of database design. Because if there is a customer’s account, it is not restricted by the database design to not be stored in Services table etc. Now we can keep all transfers in one table only since Accounts are unified among all the entities.
Keep the balance information in the table primary Entities table and separate tables for all transfers. Here for all kind of transfers between the entities, we are keeping separate tables. For example, a transfer between a Customer and Service provider will be stored in a table called “Spending”. Another table will have transfer data for transfer between Service and Dealers called “Commission” etc. In this case, we are not storing all the transfers of the funds in a single table, but the foreign keys are properly defined since the tables “Spending” and “Commission” are only between two specific entities.
According to the best practices, which one of the above given solutions is correct, and why?
If you are simply looking for schemas that claim to deal with cases like yours, there is a website with hundreds of published schemas. Some of these pertain to storing transaction data concerning customers and suppliers. You can take one of these and adapt it.
http://www.databaseanswers.org/data_models/
If your question is about how to relate accounts to business contacts, read on.
Customers, Services, and Dealers are all sub classes of some super class that I'll call Contacts. There are two well known design patterns for modeling sub classes in database tables. And there is a technique called Shared primary Key that can be used with one of them to good advantage.
Take a look at the info and the questions grouped under these three tags:
single-table-inheritance class-table-inheritance shared-primary-key
If you use class table inheritance and shared primary key, you will end up with four tables pertaining to contacts: Contacts, Customers, Dealers, and Services. Every entry in Contacts will have a corresponding entry in one of the three subclass tables.
An FK in the accounts table, let's call it Accounts.ContactID will not only reference a row in Contacts, but also a row in whichever of Customers, Dealers, Services pertains to the case at hand.
This may work outwell for you. Alternatively, single table table inheritance works out well in some of the simpler cases. It depends on details about your data and your intended use of it.
You can make table Accounts with three fields with FK to Customers,Dealers and Services and it's will close problem. But also you can make three table for each type of entity with accounting data. You have the deal with multi-system case in system design. Each system solve the task. But for deсision you need make pros and con analyses about algorithm complexity, performance and other system requirements. For example one table will be more simple to code, but three table give more performance of sql database.
Consider we have a database that has a table, which is a record of a sale. You sell both products and services, so you also have a product and service table.
Each sale can either be a product or a service, which leaves the options for designing the database to be something like the following:
Add columns for each type, ie. add Service_id and Product_id to Invoice_Row, both columns of which are nullable. If they're both null, it's an ad-hoc charge not relating to anything, but if one of them is satisfied then it is a row relating to that type.
Add a weird string/id based system, for instance: Type_table, Type_id. This would be a string/varchar and integer respectively, the former would contain for example 'Service', and the latter the id within the Service table. This is obviously loose coupling and horrible, but is a way of solving it so long as you're only accessing the DB from code, as such.
Abstract out the concept of "something that is chargeable" for with new tables, of which Product and Service now are an abstraction of, and on the Invoice_Row table you would link to something like ChargeableEntity_id. However, the ChargeableEntity table here would essentially be redundant as it too would need some way to link to an abstract "backend" table, which brings us all the way back around to the same problem.
Which way would you choose, or what are the other alternatives to solving this problem?
What you are essentially asking is how to achieve polymorphism in a relational database. There are many approaches (as you yourself demonstrate) to this problem. One solution is to use "table per class" inheritance. In this setup, there will be a parent table (akin to your "chargeable item") that contains a unique identifier and the fields that are common to both products and services. There will be two child tables, products and goods: Each will contain the unique identifier for that entity and the fields specific to it.
One benefit to this approach over others is you don't end up with one table with many nullable columns that essentially becomes a dumping ground to describe anything ("schema-less").
One downside is as your inheritance hierarchy grows, the number of joins needed to grab all the data for an entity also grows.
I believe it depends on use case(s).
You could put the common columns in one table and put product and service specific columns in its own tables.Here the deal is that you need to join stuff.
Else if you maintain two separate tables, one for Product and another for Sale. You use application logic to determine which table to insert into. And getting all sales will essentially mean , union of getting all products and getting all sale.
I would go for approach 2 personally to avoid joins and inserting into two tables whenever a sale is made.
I'm new to databases. I have 4 tables in total: 3 tables are populated automatically when the user logs on to Facebook. I want the values of the primary keys form those tables to be populated into the 4th table. How do I do this... I need help soon!
This is how the tables look:
table:attributes
fb_user : fb_uid, birhtday, gender, email.
company_master : com_id, com_name.
position_master : pos_id, pos_name.
And the 4th table goes like this:
[table]:[attributes]
work_history : work_id, fb_uid, com_id, pos_id.
fb_uid, pos_id and com_id are primary keys.
How to perform this using less database operations? Is there any way to use triggers for this to optimize?
Firstly what type of database are you using? Secondly, this seems to be a database design issue. You really should use a single unique primary key across all tables instead of using different primaries and mapping them. Since your using Facebook it would make sense to use their Facebook id as the primary for all tables then store the other ids as unique fields. This would also allow you to easily use useful features like joins to retrieve data from multiple tables at once. If this isn't practical, since for example, your using multiple logins (Facebook Google, etc) for the same user, you would then want to have a lookup table like you suggest as the driving table then use it to help populated the others. Ideally you want to minimize redundant data as much as possible to reduce the risk of data inconsistencies. If you are new to databases you should do some reading on database design and database normalization. A good design will help with scalability and prevent a lot of headaches and frustration.
If you had to design a database with paid users and trial users would you put them in the same table and differentiate between them with a field? Or would you put them in two separate tables?
Or would you do the best of both worlds and put them in the same table but create two views 1) PaidUsers and 2) TrialUsers
Thanks!
I just express some performance considerations in following opinions.
In single user query(ex. login check, or data retrieving for single user), there are not significant differences between these two strategies.
But if you need some statistic data, for example, one for paid users and another for trial users. And seperating to two tables may be a good idea.
Otherwise, if you need some statistic data whatever paid users or trial users, single table may be a good idea.
What if you need both of scenarios? Well, I think that would be a case which some common attributes exist between two kinds of users.
These common attributes should be put in one table, and dedicated attributes for particular users should be put in 'sub-table' inheriting from former table. Just as vonPetrushev said.
Since your paid users would probably be related to some additional data, but still have the same fieldset as non-paid, the correct way to do this is [is-a] approach:
User
id
username
password
fullname
...
Paiduser
user_id [fk->User::id]
account_id
.... [other addidional data]
EDIT: Now, the trial users will be all records in User that does not have entry in Paiduser. I'm assuming that Paiduser fieldset is a superset of the fieldset of a trial/normal user [User].
EDIT 2: To get a list of trial users, which are 'set difference' between User and Paiduser, the following sql should work:
select u.*
from (User as u
join Paiduser as p on u.id<>p.user_id)
The best solution may depend on database type. My experience is with MySQL and SQL Server. I've always put all users into a single table. Then differentiate as needed using fields. This could apply to paid/ unpaid or anything else. This solution meets 3NF standards and seems easier to me for maintenance etc. What reason would there be to use multiple tables?