I am creating a database which due to college security rules has to be an access database :( but its a website database and i have an invoiceing system. I have an user and product table and i am trying to add a comment table which relates to both of the these tables via the fields UID(user id) & PID(product id). however both of these field are already related to the invoice table. im sorry if this seems like a stupid question but i couldnt find a clear answer on this.
There is nothing saying that you can't have two tables that use the same foreign keys from two other tables. But, you need to ask yourself what you are trying to represent.
Are you trying to make arbitrary comments about each user and each product, or are you really trying to attach comments to an invoice line? If that is the case, then you should probably either put the comment in the Invoice table, or make a foreign key relations ship with that.
In the attached diagram I show both ways a Comments table could be related.
Related
I have the following partial database design:
All the tables are dependent on each other so the table bvd_docflow_subdocuments is dependent on the table bdd_docflow_subsets
and the table bvd_docflow_subdocuments is dependent on bvd_docflow_subsets. So I thought I could me smart and use foreign keys on every table (and ON DELETE CASCADE). However the FK are being drilldown how further I go in to the tables.
The problem is the table bvd_docflow_documents has no point having a reference to the 1docflow_documentset_id` PK / FK. Is there a way (and maybe my design is crappy) that only the table standing above it has an FK relationship between the tables and not all the tables above it.
Edit:
More explanation:
In the bvd_docflow_subsets table information is stored about objects to create documents. There is an relation between that table and bvd_docflow_subdocuments table (This table stores master data about all the documents for an subset. (docflow_subset_id is in both tables). This is the link between those to tables.
Going further down we also got the table bvd_docflow_documents this table contains the actual document data. The link between bvd_docflow_documents and bvd_docflow_subdocuments is bvd_docflow_subdocument_id.
On every table I got an foreign key defined so when data is removed on a table all the data linked to that data is also removed.
However when we look to the bvd_docflow_documents table it has all the foreign keys from the other tables (docflow_subset_id and docflow_documentset_id) and there is the problem. The only foreign key needed for that bvd_docflow_documents table is docflow_subdocument_id and no other.
Edit 2
I have changed my design further and removed information that I don't need after initial import of the data.
See the following link for the (total) databse design:
https://sqldbm.com/Project/SQLServer/Share/_AUedvNutCEV2DGLJleUWA
The tables subsets, subdocuments and documents have a many to many relationship so I thought a table in between those 3 documents_subdocuments is the way to go were I define all the different keys for those tables.
I am not used to the database design first and then build it. But, for everything there is a first time, and I try to do make a database that is using standards and is using the power of SQL Server the correct way.
I'll address the bottom-most table and ignore the rest for the most part.
But first some comments. Your schema is simply a model of a system. To provide feedback, one must understand this "system" and how it actually works to evaluate your model. In addition, it is important to understand your entities and your reasons for choosing them and modelling them in the specified manner. Without that understanding all of this guessing based on experience.
And another comment. Slapping an identity column into every table is just lazy modelling IMO. Others will disagree, but you need to also enforce all natural keys. Do you have natural keys? It is rare not to have any. Enforce those that do exist.
And one last comment. Stop the ridiculous pattern of prepending the column names with the table names. And you should really think long and hard about using very long table names. Given what you have, I sense you need a schema for your docflow stuff.
For the documents table, your current PK makes no sense. Again, you've slapped an identity column into the table. By itself, this column is a key for the table. The inclusion of any other columns does not make the key any more "unique" - that inclusion is logical nonsense. Following your pattern, you would designate the identity column as the primary key. But ...
According to your image, the documents table is related to one and only one subdocument. You added a foreign key to that table - which matches the image. You also added additional columns and foreign keys to the "higher" tables. So now a document "points" to a specific subdocument. It also points to a specific subset - which may have no relationship to the subdocument. The same thought applies to the other FK. I have a doubt that this is logically correct. So why do these columns (and related FKs) exist? Perhaps this is the result of premature optimization - which everyone knows is the root of all evil coding. Again, it is impossible to know if this is "right" or even "useful" for your model.
To answer your question "... is there a way", the answer is obviously yes. You remove the columns of which you complain. You added them - Why? Is this perhaps a problem with the tool you are using?
And some last comments. There is nothing special about "varchar(50)". Perhaps this is a place holder that will be updated later. It may also be another sign of laziness. And generally speaking, columns with names like "type" and "code" tend to be foreign keys to "lookup" tables - because people like to add, modify, or remove these sorts categorization values over time. I'm also concerned about the column name overlap among the tables. "Location" exists in multiple tables, as do action_code and action_id. And a column named "id" (action_id) suggests a lookup to another table - is it? Should it be? Is there a relationship between action_id and action_code? From a distance it is impossible to answer any of these questions.
But designing a database is more art than science. Sometimes you just need to create something, populate it with some sample data, and then determine if it works for your needs. Everyone will get something wrong in the first try. That is expected; that is how you learn. The most difficult part is actually completing your first attempt.
So I’m attempting to teach myself databases and SQL, and I’m trying to play around with making a database in management studio, and I have a question regarding recursive relationships in a table. Say I have a table called ‘Customers’ and in that table I have an int called Customer_ID as the primary key that is also an identity incrementing by 1, an nchar(125) called ‘Customer_Name’, and another int called Customer_Parent_ID (I don’t know whether I should make this an identity or not). How do I go about forming the relationships that there are customers, and I want to track that some of those customers may be parents of other customers (Think of companies, for example say both Microsoft and LinkedIn are customers, but Microsoft is also LinkedIn’s parent company and I want to show that relationship). I attached a picture of what I THINK it should look like… but again, total newbie here and any recommendations would be much appreciated.
Thank you so much!
EDIT: Added SQL Code and removed accidental mysql tag.
I think your question is somehow similar to this one, and the simple answer is you set a foreign key on Customer_Parent_ID column and refers to the Customer_ID column, so any id number that appears in the Customer_Parent_ID must also present in the Customer_ID column.
I am designing a feature for a database, but I am stuck on design.
I have a table called AgendaItems, this table is a table with Agenda Items that could be assign to possible multiple users.
Users is a table that contains a record of user names, containing a fixed amount of 17 names.
How would I design these tables possibly another table that keeps track of who is working on what Agenda Item. Keep in mind multiple users could work on an agenda Item and users could work on multiple items.
I am not sure who to design this, and wondering if it would even work?
Thanks
I don't know if I understood your problem but I think your relationship is N-N.
So, you need to create another table (UsersAgendaItems). This table must contain the AgendaItems ID and Users ID, where both of then are FK.
Your PK could be a composite PK. This way you can know what user is related with what AgendaItems.
But I don't know if that is what you want. If this is not your case, please, try to explain a little bit more!
Thanks!
I have an app where users can log comments related to any specific entity that the system has and I wanted to know if there is a "best practice" way to handle the design of the db for this kind of feature.
For example: Three current entities (tables) deal are Question, Documentation, ReferenceMaterial (self explanatory what each hold). The user can leave a comment on any one of those particular items and all comments are simply a varchar field, user id, and date of comment. EDIT: Comments can also belong to more than one entity. For example, all Question entities belong to a Quiz or Test entity. Each of those (Quiz and Test), can also have comments associated with themselves. So you could run a report to see all comments left for a test and easily just query the Comment table for every record with that test foreign key, or you could limit your query to just the comments left for questions in that test, or a particular question itself. It offered a lot of flexibility END EDIT
Right now the way that I hvae this is one Comment table with a foreign key relationship with each of the other entity tables (i.e. fkQuestion, fkDocumentation, fkReferenceMaterial, etc). So all comments in the system are stored in this table and based on what page the user is on, I conduct the join to that particular entity's records.
Is there a best practice way of doing this?
Thanks in advance for any help.
Here's the deal : this is my first ever database project and I am afraid my solution to this problem isn't quite the best. The database keeps track of different "types" of cooperators. Those types are companies, organisations, employed workers, other "persons" ...
All of those have totally different sets of information, but they all have one in common - contact information. I decided to let user enter what kind of contact information he wants to add to any of the cooperator, whether its e-mail, phone, URL, Fax and so on ...
So I created "Contacts" table in which all the contact data for all the cooperators will be put, regardless of what type the cooperator is it.
The TablesList is the table that contains the list of cooperator types (Companies, Organisations, Workers)
Each row in the Contacts table must contain "TableID" number which identifies what type of the cooperator is it (Company/Worker/Organisation...), and must contain "RowID" which identifies what exact company/worker/organisation the contact is about.
The problem that exists it that Contacts table contains foreign keys from 3 other tables in 1 column, which cannot be good. I could remove the relationships and just fill the column with thos ID's without the DBMS knowing about the constrains, but that just doesnt look like a good solution to me, so now I doubt this idea is any good.
What do you suggest ?
Keep in mind that in future there may be some more types of cooperators added if needed (like temp/contract workers, agencies) and Contacts table should be designed to support them too
Thanks in advance !
Btw im using SQL CE and C#
here is the sketch of whats going on :
EDIT
Although it doesnt feel right, I just removed the relationships and it works just fine with my application so far
I suspect your design is over-normalized. You can simplify it by consolidating data into three tables: Companies, Workers and Organisations. It's not going to be normalized but it is much simpler to work with.
Check out http://www.codinghorror.com/blog/2008/07/maybe-normalizing-isnt-normal.html