I'm looking to create a database for tracking purposes. For the purposes of this question I have abstracted it a bit and transformed it into a Product Design tracking database.
I'm trying to make it as normalized and efficient as possible.
Essentially I want to be able to track Employees and what designs they've participated in.The queries I want to run aren't particularly complex. I want to be able to query how many employees participated in the design of a specific model, what models and products an employee has designed, how many employees designed a product, etc. The products would be redesigned every year or half year.
My concern is how I'm managing the many to many relationship between models and employees. In the example provided I have a Design table between the Model and Employee Table. This will essentially be a dump of all Employees designers, which both resolves the many to many relationship (which I understand to be a bit of a bad thing to have) and make query design relatively simple. I also assume I can index it by either Emp_ID or Model_ID to make it more efficient.
However I'm worried this table may get a bit unwieldy over time. In its current role I could make this database very inefficient and probably not notice any degradation in performance. However I'm hoping to make this relatively scale-able as I want to make this easy to admin (whether I admin it or someone else takes over) and I'm hoping to add features over time (a CRM-like functionality for example).
I was thinking I could create a table to for each employee and track design projects by having them in a separate empID_design table, but that also seemed very unwieldy. Essentially every other way I thought up on how to do this ended up with creating a large number of tables versus inserting a Row.
One other thing was I wanted to be able to track project managers. In the current form I thought tracking it in the Design table made sense. I don't think the Project Mgr would change mid-design but is there an elegant way to track it if they did?
Any help or advice you can provide is appreciated. I'm a bit rusty with Database Design and ERD Design, so if you notice something that doesn't make sense, its more likely a mistake I made as opposed a fancy nuanced design I thought up.
To give a basic idea of what each table could be representing:
Company: Black and Decker
Product: Rotary Tool
Model: D-5230
Designed by: George Santos, Kevin Smith, John Rodes
Project Manager: Kevin Smith
Thank you in advance!
ERD Diagram: http://i.stack.imgur.com/flo4l.png
It sounds to me like the intersection table between model and employee ought to be a role table, in which each row has:
An employee ID
A model ID
A role ID: designer, project manager, lead designer, etc
In that way an employee could even have multiple roles on a project.
Related
I am creating a mobile game where I am optimistically hoping i'll have millions of players.
I have created a users table that currently has roughly 8 columns (ie. userid, username, password, last_signin, etc)
For every user I'll also need to record the amount of in-game currency they have (ie. gold, silver, gems, etc).
This is a 1:1 relationship (a user will only ever have 1 value defining how much gold they have).
I am no database expert (which is why I am posting here). I worry If I added the gold, silver, gems, etc as new rows in the users table that the users table will be hammered with a crazy amount of queries per second. Everytime someone in the game finds more gold, more silver, logs in, creates an account... the users table will be accessed and/or updated.
Would it be smarter to add the gold, silver, and gems as columns in a new table called "resources" that had the following columns : userid, gold, silver, gems. This new table would have the exact same number of rows as the user table since there is a 1:1 relationship between users and resources. I'm wondering if those queries would be faster since the database data is split up and not all queries would go to the same table.
Clearly to me it seems better to put it all in 1 table since they are 1:1.... but It also seemed like a bad idea to have the majority of the games data in 1 table.
Thanks for any advice you can give!
Ryan
There are plenty of cases where good design calls for two tables in a 1:1 relationship with each other. There is no normalization rule that calls for decomposing tables in this manner. But normalization isn't the only handle on good design.
Access traffic is another handle. Your intuition that access to resources is going to be much more frequent than access to basic user data sounds credible. But you will need to check it out, to make sure that the transactions that access resources don't end up using basic user data anyway. It all boils down to which costs more: a fat user table or more joins.
Other responders have already hinted that there may come a day when the 1:1 relationship becomes a 1:many relationship. I can imagine one. The model of the game player gets expanded where a single user can get involved in multiple distinct instances of the game. In this case, a single user might have the same basic user data in all instances, but different resources in each instance. I have no way of telling if this is ever going to happen in your case. But, if it does, you're going to be better off with a separate resources table.
It really depends on your game design, how big your database is, and how you might expand your database in the future. I would put the resources in a separate table with a foreign key pointing to the user id because:
You can keep the user table slimmer for easier
maintenance/backup.
Simple 1-to-1 JOIN operation between two
tables doesn't take much more resources than having everything in
the same table, as long as you have proper indexing.
By keeping your tables separated, you are practicing separation of concerns;
multiple people can work on different stuff without having to worry
about affecting other tables.
Easier to expand. You may want to add other columns such as birth_date, region, first_name, etc. that
are more relevant to users' personal info to the users table in the
future. It will be confusing if columns of different purposes are
stored together. (In PostgreSQL you can't simply arrange column
order though you can create Views for that.)
This is a 1:1 relationship (a user will only ever have 1 value defining how much gold they have).
... for now ;)
I am no database expert (which is why I am posting here). I worry If I added the gold, silver, gems, etc as new rows in the users table
New columns?
Would it be smarter to add the gold, silver, and gems as columns in a new table called "resources"
Probably, because:
You'll be doing smaller writes when you update the frequently updated part, without rewriting less-modified user data
It makes it easier to audit changes to the user data
Today I was designing a database for a potential personal project of mine. Since I couldn't decide what would be a better option I asked my teacher Databases, unfortunately he couldn't tell me which of the two options is better than the other and why.
I designed the database for a dummy data generator. Since I want to generate multilangual data I thought of these tables. (But its a simplification of the tables).
(first and last)names: id, name
streets: id, name
languages: id, name
Each names.name and streets.name originates from a language, sometimes a name can have multiple origins (ex: Nick is both a Dutch as an English name).
Each language has multiple names and streets.
These two rules result in a Many-to-Many relationship. At the moment I've got only two tables, but I know I will get between 10 and 20 of these kind of tables.
The regular way one would do this is just make 10 to 20 Many-to-Many relationship tables.
Another idea I came up with was just one Many-to-Many table with a third column which specifies which table the id relates to.
At the moment I've got the design on my other PC so I will update it with my ideas visualized after dinner (2 hours or so).
Which idea is better and why?
To make the project idea a bit clearer:
It is always a hassle to create good and enough realistic looking working data for projects. This application will generate this data for you and return the needed SQL so you only have to run the queries.
The user comes to the site to get the data. He states his tablename, his columnnames and then he can link the columnnames to types of data, think of:
* Firstname
* Lastname
* Email adress (which will be randomly generated from the name of the person)
* Adress details (street, housenumber, zipcode, place, country)
* A lot more
Then, after linking columns with the types the user can set the number of rows he wants to make. The application will then choose a country at random and generate realistic looking data according to the country they live in.
That's actually an excellent question. This sort of thing leads to a genuine problem in database design and there is a real tradeoff. I don't know what rdbms you are using but....
Basically you have four choices, all of them with serious downsides:
1. One M-M table with check constraints that only one fkey can be filled in besides language and one column per potential table. Ick....
2. One M-M table per relationship. This makes things quite hard to manage over time especially if you need to change something from an int to a bigint at some point.
3. One M-M table with a polymorphic relationship. You lose a lot of referential integrity checks when you do this and to make it safe, have fun coding (and testing!) triggers.
4. Look carefully at the advanced features in your rdbms for a solution. For example in postgresql this can be solved with table inheritance. The downside is that you lose portability and end up in advanced territory.
Unfortunately there is no single definite answer. You need to consider the tradeoffs carefully and decide what makes sense for your project. If I was just working with one RDBMS, I would do the last one. But if not, I would probably do one table per relationship and focus on tooling to manage the problems that come up. But the former preference is about my level of knowledge and confidence, and the latter is a bit more of a personal opinion.
So I hope this helps you look at the tradeoffs and select what is right for you.
I have to implement a testing platform. My database needs the following tables: Students, Teachers, Admins, Personnel and others. I would like to know if it's more efficient to have the FirstName and LastName in each of these tables, or to have another table, Persons, and each of the other table to be linked to this one with PersonID.
Personally, I like it this way, although trickier to implement, because I think it's cleaner, especially if you look at it from the object-oriented point of view. Would this add an unnecessary overhead to the database?
Don't know if it helps to mention I would like to use SQL Server and ADO.NET Entity Framework.
As you've explicitly mentioned OO and that you're using EntityFramework, perhaps its worth approaching the problem instead from how the framework is intended to work - rather than just building a database structure and then trying to model it?
Entity Framework Code First Inheritance : Table Per Hierarchy and Table Per Type is a nice introduction to the various strategies that you could pick from.
As for the note on adding unnecessary overhead to the database - I wouldn't worry about it just yet. EF is generally about getting a product built more rapidly and as it has to cope with a more general case, doesn't always produce the most efficient SQL. If the performance is a problem after your application is built, working and correct you can revisit and fix up the most inefficient stuff then.
If there is a person overlap between the mentioned tables, then yes, you should separate them out into a Persons table.
If you are only tracking what role each Person has (i.e. Student vs. Teacher etc) then you might consider just having the following three tables: Persons, Roles, and a bridge table PersonRoles.
On the other hand, if each role has it's own unique fields, then you should carry on as you are and leave each of these tables separate with a foreign key of PersonID.
If the attributes (i.e. First Name, Last Name, Gender etc) of these entities (i.e. Students, Teachers, Admins and Personnel) are exactly the same then you could just make a single table for all the entities with PersonType or Role attribute added to distinguish each person's role. However, if the entities has a lot of different attributes then it would be better that you create separate tables otherwise you will have normalization problem.
Yes that is a very bad way of structuring a DB. The DB structure should be designed based on the Normalizations.
Please check the normalization forms.
U should avoid the duplicate data as much as possible, else the queries will become slower.
And the main problem is when u r trying to get data that is associated with more than one or two tables.
This is probably a simple problem for an experienced database developer, but I'm struggling... I have trouble translating a certain ER diagram to a DB model, any help is appreciated.
I have a setup similar to slide 17 of this presentation:
http://www.cbe.wwu.edu/misclasses/mis421s04/presentations/supersubtype.ppt
Slide 17 shows an ER diagram with an Employee supertype having an Employee Type attribute and as subtypes the Employee Types themselves (Hourly, Salaried and Consultant), which is very similar to my design situation.
In my case, suppose Salaried Employees are the only ones that can be bosses of other employees and I wanted to somehow indicate if a certain Salaried employee is the boss of the Hourly and/or Salaried Employee and/or Consultant (either, none or both), how could that be designed in a database model, also considering these are one-to-many relationships?
I can put a PK-FK relationship between them, which would result in all tables having two FKeys and (like Consultant having FK_Employee and FK_SalariedEmployee) and SalariedEmployee referencing itself, but I keep thinking that might not be the wisest solution....although I'm not sure why (integrity issues?).
Is this or an acceptable solution or is there a better one?
Thanks in advance for any help!
Your case looks like an instance of the design pattern known as “Generalization Specialization” (Gen-Spec for short). The gen-spec pattern is familiar to object oriented programmers. It’s covered in tutorials when teaching about inheritance and subclasses.
The design of SQL tables that implement the gen-spec pattern can be a little tricky. Database design tutorials often gloss over this topic. But it comes up again and again in practice.
If you search the web on “generalization specialization relational modeling” you’ll find several useful articles that teach you how to do this. You’ll also be pointed to several times this topic has come up before in this forum.
The articles generally show you how to design a single table to capture all the generalized data and one specialized table for each subclass that will contain all the data specific to that subclass. The interesting part involves the primary key for the subclass tables. You won’t use the autonumber feature of the DBMS to populate the sub class primary key. Instead, you’ll program the application to propagate the primary key value obtained for the generalized table to the appropriate subclass table.
This creates a two way association between the generalized data and the specialized data. A simple view for each specialized subclass will collect generalized and specialized data together. It’s easy once you get the hang of it, and it performs fairly well.
In your specific case, declaring the "boss of" FK to reference the PK in the Salaried Employees table will be enough to do the trick. This will produce the two way association you want, and also prevent employees who are not salaried from being referenced as bosses.
I'm quite new to database design and have some questions about best practices and would really like to learn.
I am designing a database schema, I have a good idea of the requirements and now its a matter of getting it into black and white.
In this pseudo-database-layout, I have a table of customers, table of orders and table of products.
TBL_PRODUCTS:
ID
Description
Details
TBL_CUSTOMER:
ID
Name
Address
TBL_ORDER:
ID
TBL_CUSTOMER.ID
prod1
prod2
prod3
etc
Each 'order' has only one customer, but can have any number of 'products'.
The problem is, in my case, the products for a given order can be any amount (hundreds for a single order) on top of that, each product for an order needs more than just a 'quantity' but can have values that span pages of text for a specific product for a specific order.
My question is, how can I store that information?
Assuming I can't store a variable length array as single field value, the other option is to have a string that is delimited somehow and split by code in the application.
An order could have say 100 products, each product having either only a small int, or 5000 characters or free text (or anything in between), unique only to that order.
On top of that, each order must have it's own audit trail as many things can happen to it throughout it's lifetime.
An audit trail would contain the usual information - user, time/date, action and can be any length.
Would I store an audit trail for a specific order in it's own table (as they could become quite lengthy) created as the order is created?
Are there any places where I could learn more about techniques for database design?
The most common way would be to store the order items in another table.
TBL_ORDER:
ID
TBL_CUSTOMER.ID
TBL_ORDER_ITEM:
ID
TBL_ORDER.ID
TBL_PRODUCTS.ID
Quantity
UniqueDetails
The same can apply to your Order audit trail. It can be a new table such as
TBL_ORDER_AUDIT:
ID
TBL_ORDER.ID
AuditDetails
First of all, Google Third Normal Form. In most cases, your tables should be 3NF, but there are cases where this is not the case because of performance or ease of use, and only experiance can really teach you that.
What you have is not normalized. You need a "Join table" to implement the many to many relationship.
TBL_ORDER:
ID
TBL_CUSTOMER.ID
TBL_ORDER_PRODUCT_JOIN:
ID
TBL_ORDER.ID
TBL_Product.ID
Quantity
TBL_ORDER_AUDIT:
ID
TBL_ORDER.ID
Audit_Details
The basic conventional name for the ID column in the Orders table (plural, because ORDER is a keyword in SQL) is "Order Number", with the exact spelling varying (OrderNum, OrderNumber, Order_Num, OrderNo, ...).
The TBL_ prefix is superfluous; it is doubly superfluous since it doesn't always mean table, as for example in the TBL_CUSTOMER.ID column name used in the TBL_ORDER table. Also, it is a bad idea, in general, to try using a "." in the middle of a column name; you would have to always treat that name as a delimited identifier, enclosing it in either double quotes (standard SQL and most DBMS) or square brackets (MS SQL Server; not sure about Sybase).
Joe Celko has a lot to say about things like column naming. I don't agree with all he says, but it is readily searchable. See also Fabian Pascal 'Practical Issues in Database Management'.
The other answers have suggested that you need an 'Order Items' table - they're right; you do. The answers have also talked about storing the quantity in there. Don't forget that you'll need more than just the quantity. For example, you'll need the price prevailing at the time of the order. In many systems, you might also need to deal with discounts, taxes, and other details. And if it is a complex item (like an airplane), there may be only one 'item' on the order, but there will be an enormous number of subordinate details to be recorded.
While not a reference on how to design database schemas, I often use the schema library at DatabaseAnswers.org. It is a good jumping off location if you want to have something that is already roughed in. They aren't perfect and will most likely need to be modified to fit your needs, but there are more than 500 of them in there.
Learn Entity-Relationship (ER) modeling for database requirements analysis.
Learn relational database design and some relational data modeling for the overall logical design of tables. Data normalization is an important part of this piece, but by no means all there is to learn. Relational database design is pretty much DBMS independent within the main stream DBMS products.
Learn physical database design. Learn index design as the first stage of designing for performance. Some index design is DBMS independent, but physical design becomes increasingly dependent on special features of your DBMS as you get more detailed. This can require a book that's specifically tailored to the DBMS you intend to use.
You don't have to do all the above learning before you ever design and build your first database. But what you don't know WILL hurt you. Like any other skill, the more you do it, the better you'll get. And learning what other people already know is a lot cheaper than learning by trial and error.
Take a look at Agile Web Development with Rails, it's got an excellent section on ActiveRecord (an implementation of the same-named design pattern in Rails) and does a really good job of explaining these types of relationships, even if you never use Rails. Here's a good online tutorial as well.