This is my first project outside of school so I'm rusty and lacking practice.
I want to create a database but I'm not sure if I'm doing ok so far. I need a little help with the reports table.
The situation:
The food bank has multiple agencies who hand out food
Each agency has to submit a report with how many families/people served from a long list of zip codes.
I thought of putting a fk on Report to Zips table. But will that make selecting multiple zips impossible?
Maybe I'm way off base. Does someone have a suggestion for me?
A better name for this table might be FoodService or something. I imagine the kind of reports you really want to end up are not just a single row in this table, so naming it Report is a bit confusing.
In any case, each Report is the unique combination of {Agency ID, ZIP code, Date} and of course Agency ID is a foreign key. The other columns in this table would be number of families and people served, as you've indicated. This means you'll have rows for each agency-ZIP-date combination like this:
Agency | ZIP | Date | FamiliesServed | PeopleServed
Agency A | 12345 | Jan-12 | 100 | 245
Agency A | 12340 | Jan-12 | 20 | 31
Agency B | 12345 | Jan-12 | 80 | 178
Agency B | 12340 | Jan-12 | 0 | 0
Are these totals also broken down by "program"? If so, program needs to be part of the primary key for this table. Otherwise, program doesn't belong here.
Finally, unless you're going to start storing data about the ZIP codes themselves, you don't need a table for ZIP codes.
Usually having orphan tables like "Food" is a sign something's missing. If there's that much data involved, you'd think it would link in to the order model in some capacity, or at the very least you'd have some kind of indication as to which agency stocks which kind of food.
What's curiously absent is how data like "families-served" is computed from this schema. There doesn't seem to be a source for this information, not even a "family served" record, or a spot for daily or weekly summaries to be put in and totalled.
A "Zips" table is only relevant if there is additional data that might be linked in by zip code. If you have a lat/long database or demographic data this would make sense. Having an actual foreign key is somewhat heavy handed, though. What if you don't know the zip? What if, for whatever reason, the zip is outside of the USA? How will you handle five and nine digit zip codes?
Since zips are not created by the user, the zips table is mostly auxiliary information that may or may not be referenced. This is a good candidate for an isolated "reference" table.
Remember that the structure of a diagram like this is largely influenced by the front-end of the application. If users are adding orders for food items, that translates into relationships between all three things. If agencies are producing reports based on daily activity logs, then once again you need relationships between those three entities.
The front end is usually based on use-cases, so be sure you're accommodating all of those that are relevant.
Related
I need to refactor an old mysql database of products, which is divided into tables that store characteristics of different types of products.
That is to say, not all products have the same number of characteristics, and some of them influence the price of the product while others do not. So I don't see clearly if need a pivot table to manage relations between products and its features.
I can represent this as a hardware store where there are everything from screws to tools, going through some materials such as iron and wood.
For example, if we consider screws, under the name screw we have different sizes and types (for wood, for metal, millimeter thread or self-drilling), each size and type combination will determine a price, but maybe the color of the screws don't affect prices
So I was thinking of the following table structure:
products:
id | name_id | feature_id | price
product_names:
id | name
product_features:
id | name | description
But it is not clear to me how to deal with the situation that a product may have more than one feature and not all are relevant for it's price.
Thank you for any suggestion.
Based on the exchange of opinions, I arrived at this concept of a diagram. I would like to know if you see it as appropriate.
I am working with a client in manufacturing whose products are configurations of the same bunch of parts. I am creating a database that holds all valid products and their Bill of Materials. I need help on deciding a Bill Of Material schedule to implement.
The obvious solution is a many-to-many relationship with a junction table:
Table 1: Products
Table 2: Parts
Junction Table: products, parts, part quantities
However, there are multiple levels in my client's product;
-Assembly
-Sub-Assembly
-Component
-Part
and items from lower levels are allowed to be associated with any upper level item;
Assembly |Sub-assembly
Assembly |Component
Assembly |Part
Sub-Assembly |Component
Sub-Assembly |Part
Component |Part
and I suspect the client will want to add more levels in the future when new product lines are added.
Correct me if I am wrong, but I believe the above relation schedule would demand a growing integer sequence of junction tables and queries (0+1+1+2+3...) to display and export the full Bill of Materials which may eventually affect performance.
Someone suggested to put everything in one table:
Table 1: Assemblies, sub-assemblies, components, parts, etc...
Junction table: Children and Parents
This only requires one junction table to create infinite levels of many-to-many relationships. I don't know if I trust this solution, but I can't think of any issues other than accidentally making an item its own parent and creating an infinite loop and that it sounds disorganized.
I lack the experience to determine whether either or neither of these models will work for my client. I am sketching these models in MS Access, but I am open to moving this project to a more powerful platform if necessary. Any input is appreciated. Thank you.
-M
What you are describing is a hierarchy. As such it should take the form:
part_hierarchy:
part_id | parent_part_id | other | attributes | of | this | relationship
So part_id 1 may have a parent part_id 10 "component" which may have a parent_part_id (when looked up itself in this table) of 12 "Assembly. It would look like:
part_id | parent_part_id
1 | 10
10 | 12
and parts table:
part_id | description
1 | widget
10 | widget component
12 | aircraft carrier
That's a little simplified since it doesn't take into account your product/part relationship, but it will all fit together using this methodology.
Nice and simple. Now it doesn't matter how deep the hierarchy goes. It's still just two columns (And any extra columns needed for attributes of this relationship like... create_date, last_changed_by_user, etc.
I would suggest something more powerful than access though since it lacks the ability to pick a part a hierarchy using a Recursive CTE, something that comes with SQL Server, Postgres, Oracle, and the like.
I would 100% avoid any schema that requires you to add more fields or tables as the hierarchy becomes deeper and more complex. That is a path that leads towards pain and regret.
Since the level of nesting is arbitrary, use one table with a self-referencing parent_id foreign key to itself.
While this is technically correct, navigating it requires recursive query that most DB's don't support. However, a simple and effective way of making accessing nested parts simple is to store a "path" to each component, which looks like a path in a file system.
For example, say part id 1 is a top level part that has a child whose id is 2, and part id 2 has a child part with id 3, the paths would be:
id parent_id path
1 null /1
2 1 /1/2
3 2 /1/2/3
Doing this means finding the tree of subparts for any part is simply:
select b.part
from parts a
join parts b on b.path like concat(a.path, '%')
where a.id = ?
Hi I've got a small internal project I am working on. Currently it only serves my company, but I'd like to scale it so that it could serve multiple companies. The tables I have at the moment are USERS and PROJECTS. I want to start storing company specific information and relate it to the USERS table. For each user, I will have a new column that is the company they belong to.
Now I also need to store that companies templates in the database. The templates are stored as strings like this:
"divider","events","freeform" etc.
Initially I was thinking each word should go in as a separate row, but as I write this I'm thinking perhaps I should store all templates in one entry separated by commas (as written above).
Bottom line, I'm new to database design and I have no idea how to best set this up. How many tables, what columns etc. For right now, my table structure looks like this:
PROJECTS
Project Number | Title | exacttarget_id | Author | Body | Date
USERS
Name | Email | Date Created | Password
Thanks in advance for any insights you can offer.
What I would do is create 2 tables:
I would create one table for the different companies, lets call it COMPANY:
Company_id | Title | Logo | (Whatever other data you want)
I would also create one table for the settings listed above, lets call it COMPANY_SETTINGS:
Company_id | Key | Value
This gives you the flexibility in the future to add additional settings without compromising your existing code. A simple query gets all the settings, regardless of how many your current version uses.
SELECT Key, Value FROM COMPANY_SETTINGS WHERE Company_id = :companyId
Te results can then be put into an associative array for easy use throughout the project.
I having a question about same FK using in the schema. Here is the question
|=======================================|
| Book |
|=======================================|
| Book_ID (PK)| Cover_Paper | Page_Paper|
|-------------|-------------|-----------|
|====================================|
| Paper |
|====================================|
| Paper_ID (PK)| Paper_Type | weight |
|--------------|------------|--------|
Let say, I have different type of paper with different weight use to print cover and page.
So I need to plug the Paper_ID as FK into Book table. The problem is, it is wrong to have different column name as FK. If I change the table to the same column name it will be so weird.
|==========================================|
| Book |
|==========================================|
| Book_ID (PK)| Paper_ID(FK) | Paper_ID(FK)|
|-------------|--------------|-------------|
Any help on this problem??
It's not wrong to have column names that differ from the domain name of the column. In fact, it is often necessary.
The alternative - having two columns with the same name - is bad. How would you know which column indicated cover paper and which page paper? By position? This ties the meaning of the content to the physical representation of the data. What happens if I select Book_ID and just one of the Paper_ID columns? One wouldn't know, without additional external information, what the data means. Rather, that additional information should be part of the representation, so that it's as self-descriptive as possible.
In relations where each role is filled by a unique domain, it's easy enough to just use the name of the domain as the name of the role without confusion. If a book consisted of a single type of paper, talking about the book's paper makes sense. Same for a bicycle's seat and a person's nose.
However, when a relation has more than one of the same kind of thing, we need to indicate each thing's role. Distinguishing Cover_Paper and Page_Paper like you did is the right way to do it. (It's too bad SQL DBMSs don't have separate role and domain names for each column, but I digress.)
You could call it Cover_Paper_ID and Page_Paper_ID, it's sort of an industry convention to attach ID to surrogate identifier columns though I think it reads better without. In other relations, it's often sufficient to write just the role without the domain - e.g. in a Marriage we might have columns for Husband and Wife, instead of writing Husband_Person and Wife_Person.
Both Edgar Codd (author of A Relational Model of Data for Large Shared Data Banks) and Peter Chen (author of The Entity-Relationship Model - Toward a Unified View of Data) discuss roles in their papers. I highly recommend studying both, especially since very few online resources ever mention the topic.
I am creating a database for a publishing company. The company has around 1300 books and around 6-7 offices. Now i have created a table that displays the stock items in all locations. The table should look like following to the user:
Book Name Location1 Location2 Location3 ......
History 20000 3000 4354
Computers 4000 688 344
Maths 3046 300 0
...
I already have a Books table which stores all the details of the books, i also have a office table which has the office information. Now if i create a stock management table which shows the information like above i will end up in a huge table with a lot of repetition if i store my data in the following way:
Column1- Book_ID Column2- Location_ID Column3- Quantity
1 1 20000
1 2 3000
1 3 4354
2 1 4000
2 2 688
...
So, i think this isn't the best way to store data as it would end up with 1300 (Books) X 7 (Locations) = 9100 rows. Is there a better way of storing data. Now i can have 7 additional columns in the Books stable but if i create a new location, i will have to add another column to the Books table.
I would appreciate any advice or if you think that the above method is suitable or not.
Nope, that's the best way to do it.
What you have is a Many-to-Many relationship between Books and Locations. This is, in almost all cases, stored in the database as an "associative" table between the two main entities. In your case, you also have additional information about that association, namely, it's "stock" or "quantity" (or, if you think about it like a Graph, the magnitude of the connection, or edge-weight).
So, it might seem like you have a lot of "duplication", but you don't really. If you were to try to do it any other way, it would be much less flexible. For example, with the design you have now, it doesn't require any database schema change to add another thousand different books or another 20 locations.
If you were to try to put the book quantities inside the Locations table, or the Locations inside the Books table, it would require you to change the layout of the database, and then re-test any code that might be use it.
Thats the most common (and effective) solution. Most frameworks like Django, Modx and several others implement Many2Many relations via an intermediate table only, using foreign key relations.
Make sure you index your table properly.
ALTER TABLE stock_management add index (Book_ID), add index (Location_ID)
That really the best way to do it; you have 9100 independent data to store, so you really do need 9100 rows (less, really; the rows where the quantity is 0 can be omitted.) Other way of arranging the data would require the structure of the table to change when a location was added.