Questions tagged [relational-theory]

On this site this tag applies to questions about Relational Model theory. The Relational Model for database management is an approach to managing data using a structure and language consistent with first-order predicate logic. In the Relational Model of a database, all data is represented in terms of tuples, grouped into relations. A database organized in terms of the Relational Model is a relational database.

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What's the best database if i want save data temporally? [closed]

I want to create a datalog system so I need to store some int data temporally. What would be the best database (Relational, NO-SQL or some specific) for that purpose? And what would be the best way to ...
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In terms of relational databases is a Relvar the equivalent to a Schema?

I've been reading up on relational databases and the term Relvar and schema keeps coming up. From my understanding: A relvar is a variable holding a relation. A schema is a logical definition of a ...
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What are the different types of binary relationship types?

I'm new to databases and while studying questions on it, I've come across one that I can't find the answer to. Define the three different binary relationship types that are common in relational ...
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922 views

How to insert values into a junction table?

I add values into my two tables using the code below, but I also have a junction table called book_main_cover and I want to add data into this table to make a connection between book_id and ...
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1answer
32 views

Relation between tables [closed]

This question may be too easy to ask, but I can't understand how to do it. I am new in SQL. I have two tables. Table I book_id (AI & Primary Key) book_name book_year Table II ...
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3k views

Create relationship between two tables with composite primary key

I've created a table [t1] with two fields and a composite primary key, show in below: create table t1( id int, name nchar(10), primary key(id,name) ); I want to create a second table [t2]...
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2answers
741 views

SQL Query: Selecting a person who is a member of all existing groups

I'm tinkering around with my very first SQL queries and am completely baffled by a problem I encountered. Let's say I have the following database: PERSON(PID, Name) MEMBER(PID, GroupID) How would I ...
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MongoDB Manual References vs DBREF

I've been researching MongoDB and trying to see if it would be a fit for my company's product catalog. I came across database references: http://docs.mongodb.org/manual/reference/database-references/ ...
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MongoDB/MySQL - auto increment vs object ID

I am in the process of evaluating MongoDB and writing some basic PHP applications around it. Typically in my PHP/MySQL applications, I would create an ID field and set it to auto-increment on each row ...
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682 views

Help with preventing double bookings with variable lengths

I'm designing a sample database for a venue where members can create bookings for venues. I'm looking for a method to prevent double bookings (possibly by creating a button on a form that checks ...
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225 views

Help writing the following query to relational algebra

Can someone help me in writing the following query to relational algebra, I am studying DBMS and I am stuck on this exercise. Query: SELECT a.name, d.name. d.grade FROM student a, enrolled i, class ...
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Database Design for Paper Submission System

I am learner of Database design, I want to design a database for a journal paper submission system in which one paper can be submitted by one or more author. I have initially two tables Author and ...
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How to insert values in junction table for many to many relationships?

I have three tables in database: trips(trip_id(pk), trip_name(unique), user_id(fk)) places(place_id(pk), place_name(unique)) trips_places_asc(trip_id(fk), place_id(fk)) Since many trips can ...
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Need help about giving relationships in database design

I am developing a simple blog application in which users can write posts and others can like, comment, share etc. i am facing difficulty in designing database. What I have tried is: user (user_id(pk),...
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Trying to map postal codes to their respective cities, but running into some issues

The Problem I am creating a database of Countries, Regions, Cities and Postal Codes. Here's an example to give an idea of the database structure as it is now: Now, let's take Tuskegee University as ...
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332 views

Transforming a relation to 3NF

I'm trying to transform the following relation to 3NF but can't figure it out. The relation is (a student can only have 1 major): STUDENT (StuID, StuName, Major), Primary Key = {StuID} I tried the ...
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Study material for Advanced Databases module inc SQL, Relational Model, ERM & TM [closed]

For my next module in my masters, I am planning on studying Advanced Databases. (Long story short, the masters is designed for people with NON-CS degrees, so I have never studied databases, therefore ...
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A question regarding the performance of normalization

I am sorry this is such a newb question, but it is one thing I am having a difficult time wrapping my mind around, and after an evening spent reading I finally just decided to ask for some ...
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1answer
225 views

Relational Algebra Queries - How to Approach Problems?

I have the following schema: employee(sin, emp_name, emp_address, salary, supervisor_sin, dept#) works_on(emp_sin, project_number, hours) The question is: Assume that no employee works on more ...
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Multi-Tiered Database Design Issue

I am trying to build the multi-level model as demonstrated. When a user creates a campaign they will select some categories and some metros from tables Category and Metro. Those selections will then ...
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Replace relational database with “poor” design in software product with non-relational DB? [closed]

Edit: This question is about how to deal with many issues that arose from a overall system design, which made parts of the system deviate from common standards. For example, managing everything in the ...
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1answer
44 views

Is it possible to enforce a Unique Constraint on a Dataset comprised of joins

I am playing around with an idea to describe friendships in a system, and I am wondering about constraints. I currently have a database that looks like this: Users: +---------+-----------------------...
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1answer
699 views

Inheritance or lot of relationship?

I have to transpose a class Diagram into a Physical Data Model (more precisely MySQL database structure). In my class diagram, I have a lot of entities (A, B, C, D) which inherit from an other entity,...
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211 views

Best approach for Legal/Natural can have many Orders

I'm working on this model: where as you may see one NaturalPerson can have many Order and the same for LegalPerson the only difference between NaturalPerson and LegalPerson are a few so in that case ...
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Relational or non-relational database for a system to pass objects on?

hopefully this is the right place to ask this kind of question. I am working on a system that focuses on helping people give away things that they don't use anymore. So, an object typically has the ...
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86 views

Schema check or “DATE as separate table”

I'm dusting of my SQL, and would love to know if I've got my mental ER-diagram right. http://sqlfiddle.com/#!2/c5c59 Basically, I've got 10-15 different datasets (actividades) from several locations ...
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1answer
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Beginner questions about SQL and relational algebra

I'm doing some exercices waiting for the exam. I have some doubt. RELATIONAL ALGEBRA These are the table: Newspaper (Cod_n, Name_n, Publisher) Article (Cod_a, Title, Topic, ...
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660 views

Logical problem with a database model

Beforehand the table names and columns are in Spanish, my native language is Spanish. (table names have been now edited to English) I've got a database to manage the tickets sales of a trip that is ...
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1k views

What's the use of assigning foreign keys on MySQL [duplicate]

Aside from indexing the value of the foreign key, what is/are the advantage of assigning foreign keys to databases? I've seen a lot of databases that does not assign foreign keys, but is relational by ...
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1answer
3k views

3NF Decomposition - I'm not sure about this example

I am trying to make sense of an example of 3NF decomposition using the 4-step algorithm mentioned by Ullman here, but I'm not understanding what my lecturer is doing with the last step (or, worse, I'm ...
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2answers
2k views

DB Design Payments Table

I'm working on a Desktop application that uses a DB to store information i.e (customers, houses, proprietors, payments). So the application must accept payments from customers to company, company to ...
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1answer
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Schema design - Reference slightly different data in different tables

I'm trying to design a schema for a MySQL database and got stuck on the following. My database stores documents which should have relations with blocks of content. create table document ( `id` ...
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101k views

How to insert values into a table from two different tables?

I have three tables students table ------------------------------------ id(PK, A_I) | student_name | nationality teachers table ------------------------------------ id(PK, A_I) | teacher_name ...
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3answers
719 views

Heterogeneous ordered list of value

I have the following object model: class A { List<Thing> orderedListOfThings; } interface Thing { } class X implements Thing { int attr; } class Y implements Thing { String ...
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Database relationship refresher

All, After several years of programming applications, I'm looking to refresh my understanding of databases. What I knew to begin with was fairly basic, and honestly, it's disappeared over time. I ...
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2answers
150 views

Design for table with multiple links to other table

I am designing a database to keep track of our network equipment. My db has 2 tables: sites & circuits (circuit = cable) & (site = property location) Each circuit runs between two sites, so ...
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99 views

Is using a relational DB for storing votes and (accessed resources) overkill?

I am writing a forum component for a site and would like to keep track of what topics/questions a user accesses so that other topics/questions can be recommended based on said users previous choices. ...
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705 views

Parent/child relationship or not if the name of the field implies the relationship?

I am working with the harmonized system and try to catalog this in a MySQL database. This works for example like this: 01 LIVE ANIMALS 0101 horses, asses, mules and hinnies, live 0102 bovine ...
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1answer
61 views

Understanding how relationship sides works

So, I have this relations on my tables (see image) and I need to understand some things. I'll enumerate what I understand and what I need from yours is to say if I'm right or not and in case I'm not ...
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55 views

How to relate to information_schema

Is it possible to create a foreign key that relates to information_schema? For an application implementation, I would like to store extra column information in another table, but I want to ensure ...
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1answer
2k views

Difference between Relational database and time series database?

I have a bit stupid question maybe. I recently came across a term "time-series database". I would like to ask what is time series database and is it same as relational database? Thanks,
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Help required to design a database [closed]

Firstly I would like to apologies if this is not the correct place to ask this question but I know how good community spirit is around here from my time in Stack Overflow. I am very new to the world ...
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3answers
7k views

Many one-to-many relationships between two tables

In the process of creating a small database for a therapeutic boarding school with Access 2013, I have a problem when designing the relational database model. Two times at least, I ran into a ...
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Would an INNER JOIN query in a sharded relational database hit the same shard when using a compound primary key?

In this question I have asked about modulus calculation in sharded tables, this design is used: CREATE TABLE Orders (order_id INT PRIMARY KEY, ...); CREATE TABLE LineItems (order_id INT, lineitem_id ...
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1answer
9k views

Cannot add foreign key constraint while creating table

My Error Code is 1215 which finds problem with the foreign key constraint. I know all fields are the same data types. I can't see where the problem is. Any help would be much appreciated! Thanks! ...
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What would be the most efficient way to store a text messaging (SMS) database

I'm creating a database to store incoming and outgoing text messages for a program that will be responding to text messages. The app has multiple potential responses depending on the message it ...
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1answer
346 views

Transforming table to third normal form

I have a table like this: L(A, B, C, D, E) and functional dependencies are: AB -> CDE C -> D D -> B D -> E I need to transform this table into 3NF. I think it's not even in 2NF. I ...
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181 views

Is this table in third normal form?

I have a table L(A, B, C). Functional dependencies are: A->B, A->C, B->A, B->C. Is this table in 3nf? My thoughts: A and B are keys of this table. Table is in 3nf if there are no transitive ...
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Split MySql table into two tables with One to many Relationship

I have an old database table in MySql. It is used to store the orders from online ecommerce. Simplified diagram looks like this: +----+------+-----------------------+-------+--------------+ | id | ...
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Storing generated documents that can not be updated by changes in relationships

I have a system running with PostgreSQL and Yii Framework, which generates a few medical documents that, once ready, can't be changed. For example: If my full name comes out on this document today, ...