Im building a friendship site where I try and match users who share similar interests.
I have 25 questions with defined answers(drop down answers) that the user must fill out.
Im using an entity–attribute–value model to store the users id the question id the answered id the user selects.
I then use the count function to see which users have the most matches to my profile.
Current Table Structure
Question Table
Answer Table
Question_Answer_User Table
The problem im running into is I have two question and im not sure where the best place to store them is.
The question is what is your country?
The question is what is your State?
Im not sure if I should store them with the other 25 questions or if i should store them in a three separate tables as seen below.
country table
state table
user_country_state Table
There are going to be alot of answer entries for these 2 questions. For example there are 25 countries the user can answer and a total of 900 states / provinces the user can answer from.
I want to be able to consider the users location as similarity to count but im not sure what the best approach to incorporate this is?
I think the selected country and state should live in the user table, along with the other necessary user information such as name and email address. I don't think it belongs in the Answers table, but it would work there.
For the list of options for the user to select from when setting up his account, storing them in your pre-defined Q and A tables are as good a place as any. It depends, I guess, on how your data and functionality is broken apart so that you aren't crossing responsibility boundaries for the Q&A table storing survey-type answers as well as user-setup answers.
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Ok, maybe it's no the best title for the question, but this is the case.
I'm working on a project that already has an e-commerce. And part of the database looks like this. Everything works perfectly.
The problem comes with the references, if a user buys a product the shopping cart is closed, but if then the product is deleted or it's price changes the order becomes totally corrupted.
I've read this text -> Database Design for Real-World E-Commerce Systems
but I can't see the solution here.
What is the best way to do this. How big companies deal with this problem.
I mean what I need is to store all the details of an order with the data it had at the purchase moment.
There are different ways to solve this. One approach is to have a price history table rather than a price column that changes periodically. When you create an order you create it for a given price and given product. When you need to change the price of the product, instead of changing the value of the price column, you enter a new record in your price history table so future orders can then take the new price. Another approach is to decouple the product price information from the order. Rather than take the price from the product table, you have a column for unit price in the order table and the current value for the price is saved there.
As far as deleting products, it depends again on your situation. Generally it's not a good idea to delete rows that are needed for historical information. So if you no longer want to sell a product, rather than delete the record, you could have a column that has the availability of the product set to false. So previous orders would still relate to that product but new orders wouldn't be able to add it.
Every instance of every field in a table should have a 1:1 relationship with that instance of the table.
The problem is that the Price has a 1:1 relationship with the Product, which is good. But it should also have a 1:1 relationship with the Cart. And, since the price can change over time, it does not.
Two possible solutions: 1)Put a Timestamp on the Purchase, and keep all HistoricalPrices, then select the proper Price for the time of the purchase. This has the advantage of being able to tell exactly why the price changed, but can be extra work. 2)Add a PurchasePrice field to the Shopping_Cart_Products table. Assign the PurchasePrice value for that instance of that table at the time the purchase is made.
You have a few choices, if the products change while they're sitting in carts:
You update the cart and notify the user of the reason why.
You put all the information you need into the cart and work with that during checkout instead of the live product data.
Solution 1 requires you to do a sanity check at least once at the end of the checkout, to see if the cart is still valid. Solution 2 means that people may buy products that are somehow outdated.
Just got a question here about a database table. If the table only has a primary key (identity) and 1 column of useful data, is it okay to be its own table or should it be in the parent table as just the data?
The table is storing Security Questions that the user will set up with they make their account and be used to reset password in the event they want to change password or forgot the password. I have the ID of the question, and the question string in this table.
The reason I have it in its own table is that the same question could be used for many users so why store the question many times in the parent table. Thats my thinking, just wanted a few others' opinions on this.
EDIT: The Security Questions are going to be input by my team, not the user themselves. The user will pick one of the questions to use.
I would suggest this sample design using bridge table:
You can have multiple questions for a user as well as their answers unique. Also, the questions can be same for multiple users.
You must always try to prevent duplicates, that's why your solution is the best.
it will also keep your database smaller. A foreign key with int value is smaller than a string.
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I have never designed a database/data-model/schema from scratch, especially for a web-application.
In some recent job interviews, i was asked to 'design' a database for a shopping cart application. Now i am working on a mobile shopping application (retail, uses phonegap) with a backend that needs to store and process product and order info. The scale of this problem is so huge, i don't know where to start. I was hoping for some advise on -
How should I approach such a problem (shopping cart application DB) ? where should i start ?
Are there any common mistakes/pitfalls that i should avoid ?
What optimization/efficiency paradigms should i keep in mind when designing such a DB ?
How should i go about identifying entities in the problem space (products, orders, etc)? how should i derive the relationships between them ?
When a interviewer asks such a question, what exactly is he looking for ? is there something i should/should not say ?
I should also clarify that -
Yes, I am a noob, and my motives are to learn database design AND prepare for upcoming job interviews. I have read DBMS books where they describe individual concepts in detail, but i have no clue how to put those things together and start designing a database.
I have seen other threads on database design. The authors already tend to posses some knowledge on how to break the problem down. i would like to understand the methodology behind doing that.
Links to outside resources, comments, suggestions and anything that will put me on the right track is much appreciated. I hope this thread serves as a learning experience for myself and others.
There can be five tables in database:
CATEGORY this table stores information about products categories of your store and categories hierarchy.parent field of this table stores ID of the parent category.
PRODUCT all products of your store are stored in this table. This table has a foreign key categoryID which identifies ID of the category to which a product belongs.
ORDER this table stores information about all orders made by visitors of your store.
ORDERED_SHOPPING_CART table is tightly connected with PRODUCT and ORDER tables; stores information on customers' orders content.
SPECIAL_OFFER table contains a list of products, which are shown on home page as special offers
A brief answer is the way that i would tackle this problem. Firstly, there are loads of open source or free, web based shopping carts. This means that you can get one, set up the database and then have a good look around what they did.
Ask yourself questions such as, why have they done that? Why is it good? What downside could there be? How would i do it differently? why?
I would try to procure a database design tool that allows you to visualize the database. (like database designer in visual studio or i have one from MicroOlap that does pgsql databases)
Then you need to think about what you need in the database. What is the customer going to do? Buy products! Therefore you need a products table. Without going down the whole route you can see the point. Imagine what is needed, then basically make a table for it.
If you have more than one option for a field in a table, make another table with a relation in it. So if you have a product table and you have a status field. you could have more than one status. (eg out of stock, limited number, big item, expensive) instead of hard coding these fields, make a table and allow the user to add items to the table. then in the product table add a field status_id and link it to the status table
Many - many relationships are useful things to know. (i fell short to this myself.) say you have a component and product tables. The products can be made up of lots of components and the components could be allocated to many products. Create a mediator table. Something like prodcomp( and in this you would have fields like id, prod_id, comp_id, qtyneeded).
Learn to index correctly.
Don't create the database until you have a solid idea of how it will work. this saves time in recreating it later.
There may be more to this, however, i hope i have given you a good start.
My application should contain list of questions + user answers. How should I organize the database:
question1 question2 question2 ... questionN
user_id_1 yes no yes ... yes
user_id_2 no no yes ... no
...
user_id_N yes yes yes ... yes
Looks like I need to create separate table with questions and assign id to each question. How another table should look like (since number of columns is not fixed)? Or, should I have 2 more tables?
Later on I will also need to:
calculate how many users answered 'yes' on questionN;
how many friends (another table or json data) of *user_id_N* answered 'yes' on questionN.
Should I query database each for getting these numbers, or should I have separate database and keep counters there each time user answer (looks possible for item 1 only since friends list can be changed anytime).
A standard way to do this is to store each answer as a separate entity - conceptually the same as you depict, but without the requirement to modify your structure as you add new questions. Here's an example set of model definitions that achieves this:
class UserInfo(db.Model):
# Anything you want to store about the user
class Question(db.Model):
text = db.TextProperty(required=True)
# Anything else you want to store about the question
class Answer(db.Model):
user = db.ReferenceProperty(UserInfo, required=True)
question = db.ReferenceProperty(Question, required=True)
answer_text = db.TextProperty(required=True)
If you are only storing whatever what answered, you should be able to do that with 3 tables. One for your questions with a one to many to a table with the answers and then another table for the users with a one to many to the answer they provided.
Using a separate table to keep track of the questions themselves might be a good idea. By the way, if you weren't simply leaving out a header for it, your list of user IDs should itself be a specific column in the answer table. It would probably be a good idea to use a separate table to keep track of who is friends with who, though.
Also, while I'm not experienced with accessing a GAE datastore, it's fairly simple to take a count of specific answers in a single column using SQL, at least. SELECT COUNT(questionN) FROM AnswerTable WHERE questionN='yes' would be what you'd use as an SQL query.
Note that if you went with Limey's suggestion for the design, the equivalent SQL query would be more like SELECT COUNT(answer) FROM AnswerTable WHERE questionID='questionN' AND answer='yes'.
I am starting work on a project which has multiple websites for a client. For 'analytic' purposes need to measure metrics across websites over a period of time. This means i need to centralize the data model and all the possible questions/answers/lookup values so it can be used across websites. The question i have is:
Example: Age range of a user visiting website 1 is say: 30-39 years old. (We ask for age range when they enter). so in the data model I have a lookup table for answers which has all possible answers used across all websites. So (30-39) has PK ID of say 102. Now in website 2, same thing, so again (30-39) has PK of 102. This way i can measure across websites the same age range. But the problem is where or how to store the user's answer and map that to this ID?
If i have a table called say UserAnsers, it has an AgeRange colunm. Do i make this a FK to the Answer table at PK 102 to store (30-39) for the user? if yes, then what value gets written in the Useranswer table, would it be 102?
Secondly I need to measure textfields also. Like how many are complete across websites. So say "email address" field. I give this textfield a field Id of 10. Again when i write the consumer' email of say xyz#abc.com in the 'email' colunm of the the answers table how will i link this to the field ID 10?
I'd probably make an API for each website that dumps the data I want in a consistent format, which I then could load into a separate database, where I would then do the metrics on.
This gets unfeasible if the data is so large it takes hours every night to migrate the data.
But otherwise it's a solution that has the benefit that you don't have to touch the current schemas.
If the sites doesn't exist already, then I'd just force a consistent datamodel on all sites, which is trivial. It doens't matter where the mapping between "30-39" and 102 is mapped, the only thing that matters is that it's the same everywhere, which you then set up when you create the databases.
If you want the values and schemas to change a lot, then using just one database for all sites would probably be better, but if you can't do this, then make an export for each site.