# Tagged Questions

Category of database management systems characterised by the ability to join two data sets by matching on common fields, using mathematics-based relational logic.

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### complex is-A relation erd to relational schema

can some one please help me with this??? I am trying to create a relational schema for this...
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### How to map this ER model to actual tables?

Suppose we have an ER-design problem like this: A pharmaceutical company sells its products throughout a country. For the ease of sales, the entire country is divided into some Areas. Areas have ...
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### Understanding relations

Since english is not my first language i find hard to understand this paragraph that i'm reading from "Database Fundamentals" book. I'm trying to figure out, in practice, real world, what this ...
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### Relational Design - One table, two foreign keys or Two tables, one foreign key each

Looking for some advice related to optimal design in the following scenario. There is a Cases table (represents cases of inventory) There is a LocationInventory table (represents locations with ...
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### Best data modeling approch to handle redundant foreign keys in relational model

I am looking for advice on the best relational modeling approach to store surveys, questions, and responses. I am looking for which of the two approaches below looks best, or an alternative approach ...
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### Basic relational algebra question

I'm new to this and have been given a database. I've been asked to write a Basic relational algebra formula which collects failed test results with a certain teacher and display the surname and code ...
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### Two ways to define may-have-a (1..0-1) relationship

Today I have discovered for myself that may-have-a (1-0..1) relation can be implemented in two different ways. Let A be the "main" table (left side of ..) and B be the "linked" table (right side of ...
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### Finding the closure and super keys of a schema?

I am working on a problem in which I have to look at the relation R with schema R(w, x, y, z), and the three functional dependencies: w -> z ; x,y -> w ;z -> y For every non-empty subset X of ...
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### Best practice regarding concurrency for INSERT into a table with composite primary key?

Say I've got the tables users, teams and a teams_users junction table (team_ID, user_ID / composite PK). If I wanted to add a user to a team, what's the best option when it comes to performance / ...
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### Relational Model

I would really appreciate if you could check my answer for a relational model question. I just started learning. So please bear with me and please guide me through the right process. Consider the ...
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### Help with removing duplicate reversed pairs in relational algebra

I have a listing of data that contains duplicate reversed pairs and I need to remove them.. Call them, name1 and name2. Where I have Tom and Mike, and Mike and Tom, such that this single pair is being ...
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### Is my db too big for my server? Should I go nosql or stick with relational db management? [closed]

I have a mysql database that is about 22GB in size and has multiple tables with hundreds of thousands of records, my biggest table has 1.8 million records. The Database was not professionally designed ...
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### Transaction Table in Personal Finance App

I'm a noob designing a Personal Finance App to teach myself Rails. This is just for learning purposes, but I actually intend to use it to replace my current system in Google Spreadsheets. I want to ...
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### Database relation

Let's say I have 2 tables: A and B in relation one-to-one. CREATE DATABASE test; USE test; CREATE TABLE A ( a1 int, a2 int, Ab1 int, -- optional foreign key PRIMARY KEY(a1) ); CREATE TABLE B ( b1 ...
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### How to create a one to one relationship

DROP DATABASE if exists test; CREATE DATABASE test; USE test; CREATE TABLE A( a1 int not null, a2 int, PRIMARY KEY (a1) ); CREATE TABLE B( b1 int not null, b2 int, PRIMARY KEY (b1) ); How can I ...
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### Table to create Ids for one table to many table relationships

I have several tables that will represent an object that can be commented on. I would like to store all the comments in one table. To relate the other tables to the comments, I was thinking of adding ...
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### How can I re-structure my activities table?

I've created a feed but I'm not sure whether it's okay or not, hopefully will get some answers to correct it if there's anything wrong. I'm using MySQL. When a user does something, his activity is ...
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### Making database tables 1NF

I am creating a database for a DVD rental shop, I have various entities that are related to this question, such as Film, FilmStar. For each film, you record its unique number, title, the year in ...
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### Attributes in relation after cross product

I have a question regarding the resulting attributes in the cross product of two relations in relational algebra... Generally, the cross product will result in a relation whose attributes is the sum ...
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### Primary key in resulting relation from union operation in relational algebra

I have a question regarding the resulting table/relation from a union operation in relational algebra. Does the resulting relation not have a primary key? Or does it return a table with a hidden ...
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### How to remove unreferenced rows in a “Many to One” relation?

in my db i have the following entities: Cities, Persons, Houses. Each Person MUST live in a City. Each Person CAN live in a House. Each Person can change or leave their Houses. Persons living in ...
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### Do relational databases typically understand '1' and '0' as booleans?

I'm working on a code library that helps users build database searches from form inputs (a layer on top of an ORM). I want it to be compatible with most relational databases. I currently have a ...
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### 1NF vs BCNF cons and pros [closed]

I have a clue what 1NF and BCNF are, but I wonder why should someone prefer 1NF instead of BCNF? What are cons and pros with having relation in 1NF and BCNF?
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### Converting table to a 2NF relation

I'm currently going through the process of learning about database normalization & having a crack at creating my first relational database. It was going well until I hit the following problem. ...
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### Many-to-many relationship when one entity is without attributes

I'm interesting in mapping many-to-many relationship to relational model. I understand that the basic approach is to create a third table (associative entity) that connects the entities in ...
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### Sql query , please check whether my solution is correct?

Problem is: Consider the following relational schema: COURSES (cno, cname) STUDENTS (rollno, sname, age, year) REGISTERED FOR (cno, rollno) The bold attributed indicate the primary keys for ...
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### One to many relationship on a junction table

I have two entity's - Workout and Exercise. These will have a 'many to many' relationship through the junction table WorkoutExercise. Things start to get complicated when I need to have a 'one to ...
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### I have a database design for an E-commerce website. Need to know how to display related product for each specific product

For example: A customer is viewing a product on the website, say a laptop. There's a section on the left where i need to display products from the database that are associated with this particular ...
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### UPDATED: Relational (or NoSQL) Database Design

(Updated this question with more specifics. Decided on a Relational Database, and would love some comments on its design) This database holds assembly instructions data for shipbuilding, later use in ...
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I wanna store some vendors (like McDonald ,etc) and it's branches in a table. a vendor may,or may not have branches. I have created two tables: 1- A vendors table which have name,logo, etc. 2-A ...
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### How to design a Table in which its fields varies on its categories?

I am trying to design a database to post free ads. Eg http://www.gumtree.com.au/p-post-ad.html Scenario: Every ad will have different categories and some categories will have further sub categories. ...
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### Is this the correct way to model a relationship between an object which may or may not have another object?

I'm creating a database for a department store and the database has two tables: Items and Coupons. An item, like a TV, can only ever have one coupon. Some items don't have a coupon at a given time. ...
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### Decomposing a relation into 3NF/BCNF

I am having trouble decomposing a relation to 3NF/BCNF. I have determined that for the relation: R (A,B,C,D,E,F,G,H,I) where: {A -> B,C} {E -> F} {D -> I} {A,D -> G} {G -> H} ...
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### Dynamic relations in MongoDB

I'm designing a document with MongoDB where users have relationships with each other. Easy enough, right? { _id: "012", username: "happy4u", // ... related: [ '123', // user ...
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### Missing diagram option SSMS

I would like to create a relationship between to tables. Normally and in previous versions of sql server and the management studio I would go to database diagrams and draw the relation in the diagram. ...
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### Updating inverse side bidirectional association

I understand (more or less) the concept of unidirectional and bidirectional association in a relationship, but I don't see the correct practical application of it. For example, I want an contact ...
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### Table with relationship to multiple tables

I want to persist contact details for persons. This contact details can belong to a client, or a next of kin member, or whatever other entity. I'll be using Doctrine2 in a Symfony project, that will ...
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### What is the correct way to map relationships between structurally similar comments tables and commentable entities?

I'm working on the usual comments table in postgres that has a one-to-many relationship with a commentable entity. In other words, one comment belongs to a post, and a post can have many comments. ...
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### Laravel MySQL relation difficulties

I have a "users" table: And an organisations table ("orgs"): And this is the pivot table: I have some relations: On the "users" table, I have a function called "orgs()" which is a ...
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### Type of relational/object-oriented database with improved joins for object graphs?

I would like to know if there is a specific name or term for the kind of database described below: I notice one of the biggest problems when working with relational databases and object trees/graphs ...
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### I created a DB schema for a project relating to collecting comments for web pages, is relational the way to go and how are my relationships?

I'm curious if relational DB is the way to go, if the current relationships in the diagram make sense, and whether it will bode well for coding.
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I am not sure whether this is offtopic. However, please read on. A person whom I know has encountered a problem in the answer key published by CBSE, India. As their key challenging form contains a ...
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### Trying to design database for eSports Teams - Issue with dependencies

I am trying to design a database in Access for an eSport league (specifically League of Legends North America). I will post what I have and then explain my issue. My issue comes when I try to ...
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### How to model state change timeline

I've got an app where users can place orders for recurring delivery of a particular service. The orders table has columns service_id and state, where service_id links to the service the user has ...
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### Is it better to create another table to possible null values in relational databases?

I'm designing a relational database to use in MySQL. I have the next situation: In one table there are fields that in the most of situations are NULL. The fields would be like: Table name: tabla ...
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### Role based access control protocol for resources in mysql database

I have a mysql database for an application which contains users and resources, like for example books, movies, tv-shows and music. Users should be able to view and edit specific entries of this ...
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### For any SQL query, do there exists a unique translation into relation algebra

I have been studying databases and I understand that for each query that a database user type, the DBMS translate them into relational algebra operations before applying them to the database. My worry ...
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### XML vs. Relational databases?

I feel like this isn't the best question to ask on a programming site like this, but I haven't really found a satisfying answer online and I would really like to get a different perspective on this. ...