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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Sharing state across CTEs more efficiently?

Let's say I am trying to build an opinion poll app, such that I can create a template of an opinion poll, give it multiple sections/questions, assign multiple people to different copies of a given ...
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11 views

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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2answers
354 views

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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2answers
40 views

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. ...
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16 views

Using logic or in relational algebra

In relational algebra I can obtain the courses taught in Fall 2009 or Spring 2010 with Π_{course_id} (σ_{semester=“Fall” Λ year=2009} (section)) ∪ Π_{course_id} (σ_{semester=“Spring” Λ year=2010} ...
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2answers
218 views

Multiple relationships between the same entities

Is there a name for when 2 entities can have multiple relationships between them?
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1answer
21 views

What is the best way to represent an Team and player relationship in ERD

I am working on designing an ER diagram for a football system, i stopped in the relationship between the player and team, as we know the player plays for only one team and team have many players, so ...
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1answer
1k views

Number of ISA relationship triangles in an Entity Relationship Diagram

The following two diagrams are nearly identical. However, in one, there are two ISA triangles from the Entity "Movie" and in the other there is just one. What is the difference in meaning?
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2answers
184 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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7 views

table with reference to 2 other tables for ORM [migrated]

I need to have a comment table which references 2 other tables, posts, and article. 3 in total including the user_id. Comment ------- comment_id user_id article_id post_id Is this possible? I ...
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21 views

A design pattern for category features [closed]

I work for a system which has these tables: products , categories , features User wants to add some feature like color dynamically. Which of this following ways are true? First one: Product ...
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1answer
120 views

Table with multiple lookups

I bet this may be a duplicate and I'm not forming the question correctly, so feel free to point me in the right direction. Background We have a SQL Server with some legacy data. They're all ...
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18 views

Method to Obtain LossLess Join BCNF Decomposition

I have been told a way to obtain loss less join BCNF but I don't know how to calculate candidate keys(also called super key in some cases) and trivial Dependency. I have been given a relation R = ...
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1answer
40 views

Do data types go into a Relational Data Model (RDM)?

I have recently been asked to draw a Relational Data Model for a flight information database. I came up with the design in the picture below, but I was told that the drawing is not correct because ...
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3answers
114 views

What is the term for a “wide”, non-normalized view/query?

A well-designed relational DB schema tends to have a relatively large count of relatively small, normalized tables — a cluster of snowflakes, I think, describes the situation. In order to ...
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1answer
31 views

design database with 2 simillar tables

I have a database which has product_sell and product_buy tables, these two tables are different in a few fields and each one has own comment table product_sell >---< product_sell_cmt ...
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1answer
50 views

PostgreSQL JSON data type used as NOSQL, But VIEW as Relational Data Structure

Could I create a VIEW from the JSON data type but have it as a relational structure? Example: SELECT * FROM json_test; Results [ { "name": "Roy", "Country": "USA", ...
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0answers
20 views

Foreign keys in MySQL Workbench

I am defining an EER model in MySQL Workbench. I have a library with multiple copies of each book and each book has its location in the library listed in the system. When I'm creating one-to-many ...
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0answers
27 views

Normalization and multivalued attributes

I am designing a relational database in mySQL - a library management system. I want to show examples of the data in 1NF, 2NF, 3NF, BCNF, etc. My example of 1NF looks something like this 'A relation ...
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1answer
25 views

Data normalization (from 0NF to 1NF)

I am designing a relational database in mySQL - a library management system. I want to show examples of the data in 1NF, 2NF, 3NF, BCNF, etc. My example of 1NF looks something like this "A relation ...
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1answer
23 views

How Wide-columns databases achieve dynamic columns on the storage layout? [closed]

As known, in relational databases, when adding a new column, data must be reallocated (http://stackoverflow.com/questions/463677/alter-table-without-locking-the-table) to maintain a single row ...
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1answer
17 views

Groups relationships - Detailed or Direct?

I have a Person model: PersonId Name ----------- ---------------- 1 Jessica 2 Jennifer Then I have a ShareModel which have the Personand an ...
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2answers
57 views

unusual relation, binary aspect

I have question very unusual for databases. I’m not a good English speaker, but good English reader :) so for explanation I’ll give you examples. Part1 In MySQL, I have two tables with relations ...
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1answer
18 views

Determining Functional and Transitive dependencies from Relational Model (with no sample data)

I have a relational model which I've converted from an EER diagram... I've been asked to find the functional and transitive dependencies but how does one do that when there's no sample data to start ...
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1answer
70 views

How to manage many-to-many relationships when there is also a hierarchy among the many?

I have these entities – employee, task, phase, project – and these relationships: project 1:m phase phase 1:m task employee m:m task, phase, project The first two relationships form a ...
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2answers
882 views

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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2answers
57 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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1answer
22 views

sub and sub-sub item organization system [duplicate]

So I am looking to find the best database design for the following situation. I will refer to my entities as 'articles' as that would best/most-easily describe them. So the articles have already ...
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1answer
36 views

How to keep updates (diffs) of some entity in the database

What is the best way to keep updates (diffs) of the some entity in the database? At StackOverflow we can edit questions and answers. And then we can look at any revision of the question or answer we ...
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11 views

Translating duplicated data entries into Domain Relational Calculus

Given a following table named BOOKING, which contains three columns, guest_name, room_number and booking_date, how do I find the all the guest_name that have the same room_number and booking_date? I ...
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1answer
630 views

How to store several lists and their items

The app I'm working on revolves around projects. Each project can contain several lists, and each list is made up of several items. Each list relates to a single project. Is it better to have one ...
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40 views

Converting Entity Relation(ER) Model to Relational Schema?

I have the following ER Model I am trying to convert this to a relational database schema but I am not sure about several things: PORT_VISIT and PORT are weak entities. How do I figure on which ...
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0answers
11 views

Is the use of my lookup table efficient?

I'm trying to find the best way to architect the relationship in the scenario that: A team can have multiple players, a player may also have multiple teams My first thought was to use a lookup ...
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13 views

Data base design for handling website subscriptions

I have a website where at least 20 posts are posted in a day and each post contains more than 5 categories and each category has further tags. I wanted to build a subscription module that users can ...
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1answer
61 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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1answer
62 views

Suitable schema to record email sent and response received and invoicing in DB

When a form submission is made on a website: An email with form's details is sent to a set of recipients email addresses stored in a DB. The email contains a link for the recipient to show interest. ...
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2answers
332 views

Should I use a compound or surrogate PK in a many-to-many table?

I have a database: DROP TABLE IF EXISTS `books`; CREATE TABLE `books` ( `isbn` VARCHAR(255) NOT NULL, `title` VARCHAR(255) NULL DEFAULT NULL, PRIMARY KEY (`isbn`) ) COMMENT 'Books used at this ...
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1answer
73 views

Create one-to-many to two fields in different table

I have a database where I am trying to figure out how to join a table that contains an object called ModelType. The calibration table contains two fields (EffModel and BkgModel) that are based on a ...
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17 views

Medical History - Is this DB properly design?

Could you please tell me if this DB is properly design? Are relationships type correct? Is there anything I should delete or add? Thanks you all very much!
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47 views

Database schema design for individual configurations

I'm trying to design a database schema that allows me to store customer custom built products. As a simplified example: A user can buy a cupboard, draws, boxes, and dividers. A cupboard has 2 tiers. ...
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1answer
35 views

Help with relational database design

I have a data model where each user profile belongs to a department. Each job is also available for a specific department. The department names are formatted like this: AAA-BBB-CCC-DDD-EEE, but of ...
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97 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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1answer
84 views

If A and B are candidate keys, then AB is candidate key or not ?

If R{abc} is a relation, f{ a->b b->a a->c b->c }, then a and b are candidate keys. What about ab ? Is it a candidate key or is it a super key or both ?
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3answers
2k 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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44 views

MySQL Query Causing Massive Slowdown Over Time

I've been experiencing massive slowdown on my server after launching a new website. Using MONyog I can see that after an apache/mysql restart, the queries/second starts out nice and low for around 10 ...
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27 views

Database systems with users and sub users accessing the data

I am making a database for school student maintenance. Below is the basic description. There are schools. One school has many staff (i.e: Principles,Teachers, Section Head, Office Staff etc) These ...
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38 views

Designing a correct table structure

We are trying to save the Family History of a particular foreign job applicant. Below are the details we have to save. Familiy Member: Father|Mother|1st Brother| 2nd Brother| 1st Sister| etc etc ...
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21 views

How to have a relation applied only to all entities related to another given entity?

Let's say I'm trying to design an online server for judging a bunch of submissions to several problems. Firstly, each problem has many subtasks (which must go to one problem alone). For each ...
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1answer
64 views

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 ...