I'm designing the database schema for a CRM. It has the following tables: users, organizations, contacts, addresses, organization_types.
organizations might be a company, a non-profit or a individual.
users have a many to many relationship with organizations. The reason is because one company, for example, can have a salesman and a manager on the app with two different logins. On the other hand, there is the possibility that a salesman is doing sales for two different companies.
contact and addresses have a one to one relationship with organizations. My client only want a organization to have one of each of those.
I designed it in a way that a organization can also be a client, that would belong to another organization. That would mean that the organization table had a one to many relationship with itself.
That made sense to me because they seem to be the same entity. A client will also need a contacts and addresses table and it could also be a company, non-profit or individual.
The point to consider that another developer raised is that with time, it would be expensive to query the database to differentiate organizations that are our clients from the ones that are clients from our clients.
What is the best approach? Would it be better the make a client_organizations table and separate those two?
I will keep one table and create a column named parent_organization. Parent_organization will be nullable and store primary key of parent organization that child organizations belong to
Related
I have a user table setup where a user can either belong to a Supplier or a Customer organization, which can have multiple users.
My original idea for the User table was to have a customerID and a SupplierID in the user table, out of which one will be filled, based on the organization the user belongs to. This does however not feel right, but I feel like maintaining two linking tables for this is overkill as well.
What would be the best practice in this case? I do not expect there to be any more organizations added in the future, but I do want to futureproof the application, by allowing multiple users to belong to the same organization.
you can design user or organization table with a column organization type which has value: supplier/customer and a column for organizationId
I am designing a product that is mainly to be used by small organizations. The idea is for every member of the organization to have their own accounts (known as subaccounts). At the same time, there needs to be data that can be accessed by anyone with that organization. I am trying to decide between two courses of action.
Separate Table for Organizations
In this design, there would be a organizations table and a users table. The users would be connected to organizations via foreign key, and the shared data would use the foreign id of the organization.
User Conglomerate
Here an additional field in the users table would point to another row in the table (the parent) that represents the primary account for the organization and is linked to all the shared data.
Which approach would be superior in this situation?
Both approaches seem reasonable and workable, but I would lean towards having a separate table for organizations as ultimately the idea of an 'organization' is different to that of an 'user'. You may need to have different attributes for an organization than you would a user (e.g. you may need to have more than one 'superuser' for an organization at some stage), and so having this data in a separate table would make it (a) easier to code against (b) more extensible and future-proof (c) more efficient and normalized in storage.
I was studying about relationships in RDBMS.I have understood the basic concept behind mapping relation ship,but I am not able to spot them.
The three possibilities :
one to many(Most common) requires a PK - FK relationsip.Two tables involved
many to many(less common) requires a junction table.Three tables Involved
one to one(very rare). One table involved.
When I begin a project,I am not able to separate the first two conditions and I am not clear in my head.
Examples when I study help for a brief moment,but not when I need to put these principles in to practice.
This is the place where most begineers falter.
How can I spot these relationships.Is there a simpler way?
Don't look at relationships from a technical perspective. Use analogies and real-life examples when trying to envision relationships in your head.
For example, let's say we have a library database.
A library must have books.
M:M
Each Book may have been written by multiple Authors and each Author may have written multiple Books. Thus it is a many-to-many relationship which will reflect into 3 tables in the database.
1:M
Each Book must also have a Publisher, but a Book may only have one Publisher and a Publisher can publish many Books. Thus it is a one-to-many relationship and it reflects with the PublisherId being referenced in the Books table.
A simple analogy like this one explains relationships to their core. When you try to look at them through a technical lens you're only making it harder on yourself. What's actually difficult is applying real world data scenarios when constructing your database.
I think the reason you are not getting the answers that you need is because of the way you are framing the question. Instead of asking “How do I spot the correct type of relationship between entities”, think about “How do my functional needs dictate what relationship to implement”. Database design doesn’t drive the function; it’s the functional needs that drive the relationships you need to implement.
When designing a database structure, you need to identify all the entities. Entities are all the facts that you want to store: lists of things like book titles, invoices, countries, dog species, etc. Then to identify your relationships, you have to consider the types of questions you will want to ask your database. It takes a bit of forward thinking sometimes… just because nobody is asking the question now doesn’t mean that it might not ever be asked. So you can’t ask the universe “what is the relationship between these lists of facts?” because there is no definitive answer. You define the universe… I only want to know answers to these types of questions; therefore I need to use this type of relationship.
Let’s examine an example relation between two common entities: a table of customers and a table of store locations. There is no “correct” way to relate these entities without first defining what you need to know about them. Let’s say you work for a retailer and you want to give a customer a default store designation so they can see products on the website that their local store has in stock. This only requires a one-to-many relationship between a store and the customer. Designing the relationship this way ensures that one store can have many customers as their default and each customer can only have one default store. To implement this relationship is as easy as adding a DefaultStore field to your Customer table as a foreign key that links to the primary key of the Store table.
The same two entities above might have alternate requirements for the relationship definition in a different context. Let’s say that I need to be able to give the customer the opportunity to select a list of favorite stores so that they can query about in stock information about all of them at once. This requires a many-to-many relationship because you want one customer to be able to relate to many stores and each store can also relate to many customers. To implement a many-to-many relationship requires a little more overhead because you will have to create a separate table to define the relationship links, but you get this additional functionality. You might call your relationship table something like CustomerStoreFavorites and would have as its primary key as the combined primary keys from each of the entities: (CustomerID, StoreID). You could also add attributes to the relationship, like possibly a LastOrderDate field to specify the last date that the customer ordered something from a particular store.
You could technically define both types of relationships for the same two entities. As an example: maybe you need to give the customer the option to select a default store, but you also need to be able to record the last date that a customer ordered something from a particular store. You could implement the DefaultStore field on the Customer table with the foreign key to the Store table and also create a relationship table to track all the stores that a customer has ordered from.
If you had some weird situation where every customer had their own store, then you wouldn’t even need to create two tables for your entities because you can fit all the attributes for both the customer and the store into one table.
In short, the way you determine which type of relationship to implement is to ask yourself what questions you will need to ask the database. The way you design it will restrict the relational data you can collect as well as the queries you can ask. If I design a one-to-many relationship from the store to the customer, I won’t be able to ask questions about all the stores that each customer has ordered from unless I can get to that information though other relationships. For example, I could create an entity called "purchases" which has a one-to-many relationship to the customer and store. If each purchase is defined to relate to one customer and one store, now I can query “what stores has this customer ordered from?” In fact with this structure I am able to capture and report on a much richer source of information about all of the customer's purchases at any store. So you also need to consider the context of all the other relationships in your database to decide which relationship to implement between two particular entities.
There is no magic formula, so it just takes practice, experience, and a little creativity. ER Diagrams are a great way to get your design out of your head and onto paper so that you can analyze your design and ensure that you can get the right types of questions answered. There are also a lot of books and resources to learn about database architecture. One good book I learned a lot from was “Database System Concepts” by Abraham Silberschatz and Henry Korth.
Say you have two tables A and B. Consider an entry from A and think of how many entries from B it could possibly be related with at most: only one, or more? Then consider an entry from B and think of how many entries in A it could be related with.
Some examples:
Table A: Mothers, Table B: Children. Each child has only one mother but a mother may have one or more children. Mothers and Children have a one-to-many relationship.
Table A: Doctors, Table B: Patients. Each patient may be visiting one or more doctors and each doctor treats one or more patients. So they have a many-to-many relationship.
An example of one to one:
LicencePlate to Vehicle. One licence plate belongs to one vehicle and one vehicle has one licence plate.
I have the following relationships (Business rules):
User_Company : Many-to-many (multiple companies per user, multiple users per company)
Ownership : One-to-One (For each entry in relationship table, it specifies whether user is an owner or employee. If owner then a percentage must be there)
Company_ownership : One-to-many for company (Recursive relationship), as another company can also be an owner in a company, percentage must be given.
So ownership or a company can be made up of a number of companies and users.
So I have developed the following:
So does there have to be at least 4 tables for this sort of relationship or can it be simplified.
I feel it is quite complicated and would not be intuitive for another developer? How could it be optimized and elegantly arranged?
I think ownership and employment are different concepts, that would be more advised to have them separated.
Think about John who is one of the owners of A company and in the mean time he is the CTO of A.
Company and People can have a base to reduce redundancy of entities.
Based on the suggestions of Thilo
A separate relationship table was created for owners and employees respectively.
Furthermore, the company_ownership and ownership tables were removed as having a company as an owner is solved by adding an owning_user_id and owning_company_id where one will always be null. The percentage figure is added to this relationship table.
See below:
I am trying to determine how the tables need to be linked in which ways.
The employees tables is directly linked to a number of tables which provide more information. A few of those tables have even more details.
Employees have a unique employeeid but I understand best practice is to still have a id?
Customers have a unique customerid
Employees have a manager
Managers are employees
Customers have a manager associated with them. manager associated with them
Employees may have a academic, certification and/or professional information.
With all of this said what would be the best recommendation for creating primary and foreign keys? Is there a better way to handle the design?
EDIT
Updated diagram to reflect feedback thus far. See comments to understand changes taking place.
Though your question is sensible, before you go any further in design, I would suggest for you to spend some time understanding relationships, foreign keys and how they propagate through relationships.
The diagram is utterly wrong. It will help it you start naming primary keys with full name, TableNameID, like EmployeeID; then it will become obvious how keys propagate through relationships. If you had full names you would have noticed that all your arrows are pointing in the wrong direction; parent and child are reversed. Anyway, takes some practice. So I would suggest that you rework the diagram and post the new version, so that we can comment on that one. It should start looking something like this (just a small segment)
EDIT
This is supposed to point you to towards the next step. See if you can read description (specification) and follow the diagram at the same time.
Each employee has one manager, a manager manages many employees.
A manager is an employee.
Each customer is managed by an employee who acts as an account manager for that customer.
Account manages for a customer may change over time.
Each employee is a member of one team, each team has many employees.
Employee performance for each employee is tracked over time.
Employee may have many credentials, each credential belongs to one employee only.
Credential is academic or professional.
Employees have unique employeeID but I understand best practice is to
still have a id?
No. (But keep reading.) You need an id number in two cases: 1) when you don't have any other way to identify an entity, and 2) when you're trying to improve join performance. And that doesn't always work. ID numbers always require more joins, but when the critical information is carried in human-readable codes or in natural keys, you don't need a join to get to it. Also, routine use of ID numbers often introduces data integrity problems, because unique constraints on natural keys are often omitted. For example, USPS postal codes for state names are unique, but tables that use ID numbers instead of USPS postal codes often omit the unique constraint on that two-character column. In your case, you need a unique constraint on employee number regardless. (But keep reading.)
Employees have a manager.
Does the table "team" implement this requirement? If the "manager" table identifies managers, then your other manager columns should reference "manager". (In this diagram, that's customers, team, and customer_orders.)
Managers are employees.
And that information is stored in the table "manager"?
Customers have a manager associated with them.
And so does each order. Did you mean to do that?
Employees may have a academic, certification and/or professional
information.
But apparently you can't record any of that information unless you store a skill first. That doesn't sound like a good approach. Give it some more thought.
Whenever you design tables with overlapping predicates (overlapping meanings), you need to stop and sit on your hands for a few minutes. In this case, the predicates of the tables "employees" and "customers" overlap.
If employees can be customers, which is the case for almost every business, then you have set the stage for update anomalies. An employee's last name changes. Clearly, you must update "employees". But do you have to update "customers" too? How do you know? You can't really tell, because those two tables have independent id numbers.
An informal rule of thumb: if any real-world entity has more than one primary key identifying it in your database, you have a problem. In this case, an employee who is also a customer would have two independent primary keys identifying that person--an employee id and a customer id.
Consider adding a table of persons, some of whom will be employees, and some of whom will be customers. If your database is well-designed and useful, I'll bet that later some of the persons will be prospects, some will be job applicants, and so on. You will need an id number for persons, because in the most general case all you can count on knowing is their name.
At some point, you'll have to take your database design knowledge to the next level. For an early start, read this article on people's names.