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Questions tagged [relational-database]

A relational database is a digital database based on the relational model of data. This model organizes data into one or more tables (or "relations") of columns and rows

A relational database is a digital database based on the relational model of data, as proposed by E. F. Codd in 1970. A software system used to maintain relational databases is a relational database management system (RDBMS). Virtually all relational database systems use SQL (Structured Query Language) for querying and maintaining the database.

This model organizes data into one or more tables (or "relations") of columns and rows, with a unique key identifying each row. Rows are also called records or tuples.[3] Columns are also called attributes. Generally, each table/relation represents one "entity type" (such as customer or product). The rows represent instances of that type of entity (such as "Lee" or "chair") and the columns representing values attributed to that instance (such as address or price).

More to read: Relational database

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Is it ever okay to use lists in a relational database?

I've been trying to design a database to go with a project concept and ran into what seems like a hotly debated issue. I've read a few articles and some Stack Overflow answers that state it's never (or almost never) okay to store a list of IDs or…
linus72982
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Should I define the relations between tables in the database or just in code?

In my experience, many of the projects I have read in the past didn't have relationship definitions in the database, instead they only defined them in the source code. So I'm wondering what are the advantages/disadvantages of defining relations…
Yoshi
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Why does the relational model for a database matter?

I am approaching a project where I'll be having to implement a database with my boss; we're a very small start up so the work environment is deeply personal. He had given me one of the company databases before and it completely went against what I…
8protons
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Why is using MySQL for a dictionary website a bad idea?

I'm planning to design and set up a database to store dictionary entries (usually single words) and their meaning in another language. So, for example, the table Glossary must have entry and definition and each table record has a reference to the id…
Aziz Az
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What happened to database constraints?

When I review database models for RDBMS, I'm usually surprised to find little to no constraints (aside PK/FK). For instance, percentage is often stored in a column of type int (while tinyint would be more appropriate) and there is no CHECK…
Arseni Mourzenko
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Is the use of NoSQL Databases impractical for large datasets where you need to search by content?

I've been learning about NoSQL Databases for a week now. I really understand the advantages of NoSQL Databases and the many use cases they are great for. But often people write their articles as if NoSQL could replace Relational Databases. And there…
Leo Lindhorst
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Is denormalising a database for speed an anti-pattern?

I have a database with a 1:m relationship. I have to display a list of parents to the user rapidly on a home screen at startup. The parent shows a single piece of information that is a sum of a particular child field for that parent. I don’t want…
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What do relational databases gain by setting a predefined data type for each column?

I'm working with an SQL database right now, and this has always made me curious, but Google searches don't turn much up: Why the strict data types? I understand why you'd have a few different data types, for example like how differentiating between…
john doe
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How to store ordered information in a Relational Database

I am trying to understand how to properly store ordered information in a relational database. An example: Say I have a Playlist, consisting of Songs. Inside my Relational Database, I have a table of Playlists, containing some metadata (name,…
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When should you use a document vs relational vs graph database?

For the purposes of discussion let's consider a FourSquare scenario. Scenario Entities: Users Places Relationships: Checkins: users <-> places, many to many Friends: users <-> users, many to many Database Design These will most likely have…
wting
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Why many designs ignore normalization in RDBMS?

I got to see many designs that normalization wasn't the first consideration in decision making phase. In many cases those designs included more than 30 columns, and the main approach was "to put everything in the same place" According to what I…
Yosi Dahari
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Reason to prefer RIGHT JOIN over LEFT JOIN

If I understand correctly, every RIGHT JOIN: SELECT Persons.*, Orders.* FROM Orders RIGHT JOIN Persons ON Orders.PersonID = Persons.ID can be expressed as a LEFT JOIN: SELECT Persons.*, Orders.* FROM Persons LEFT JOIN Orders ON Persons.ID =…
Zev Spitz
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ERD: "many" vs "zero or many"/"one or many" crowfoot notation?

Background I saw this figure describing the different crowfoot notations used in ERD: I'm not able to find the difference between the "many" notation and the "zero or many. However I was able to find an example (see bottom left for the "many"…
KingBoomie
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Why should I use foreign keys in database?

In my 10+ years of experience in the IT field, I have never used foreign keys in any of my projects and I never felt the need. I did work with professional databases that had foreign keys constraints. I am now at a position where we are building a…
TheTechGuy
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Disadvantages of using a nullable foreign key instead of creating an intersection table

Say I have the following ER diagram: Now if I represented the relationship using a foreign key of School in Student, I could have NULL values (because a Student is not required to belong to a School), for example: So the correct way (based on what…
Tom
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