A relational database is used widely, however, not many people are aware that they are using it. What is a relational database? Why is it called “relational”? If you think that the database name comes from the word “relation” you are right.
But in the case with a database, “relation” is a kind of a table organized in a special two-dimensional way. This table is the main storage unit of relational databases. So, when it comes to a relational database definition, it could sound like this: this database is a set of multiple data representing related information arranged in a special way.
The entire database can consist of one or some of such relations, or two-dimensional tables. In tables, different records can be stored. The records are filled in the table not randomly but according to particular rules. These rules and principles are the base for a relational database model.
You can assess and reassemble the data from such a database without changing or reorganizing the tables. This database is used now for many apps. However, a database serves as a foundation for an app, users cannot see it.
Relational Database Model: Relations and Principles
Initially, data was organized in a particular kind of hierarchical structures, and just in 1970, E.F. Codd suggested a different data organization way: in rows and columns. Each column contains one or several data categories. And each row containes a unique data instance that identifies data which is contained in a column. It is also called a key.
There is also a primary key. It is unique to a table and provides the identification of information contained in the table. Here is where relation can be established. In the table, a foreign key can be placed. This foreign key is a field in the table that provides a link to a data instance which is unique, a key in a different table.
So, the main features of relational databases are:
- Data is arranged in a special table as a system or relations
- A separate relation is arranged in a separate table
- Columns indicate each table entity
- Rows are represented by a unique single entity
In each table, a super key, or a primary key, is contained, it provides the identification for each entity.
How Does a Relational Database Work and What Can You Do with It?
Now, some words about how it all works and how the needed data can be searched in the tables. Do you remember about the foreign key? This is the main part of the relational model because it creates a relation between the tables. It allows for pulling related data from different tables. For example, a field in one table uses the same data set as another table does. With a foreign key, you can pull the data from the same set in both tables.
For example, you have to calculate the price for products that a customer buys. Different products are indicated in different tables, but the related fields usually have the same names in all tables. For example, if you are searching for products, you, most likely, will find them under the keys “Product ID”, “Product Price” in all tables. You can pull data about the products from the indicated tables and calculate, for example, the total sum to be paid by the customer.
The main operations that you can perform with a relational database are the following:
- You can select values based on the criteria provided in advance
- You can show values of all attributes that you have selected
- You can combine information pulled from different tables
- You can view rows with similar information set from all tables
- You can combine rows and remove them from all related tables
- You can search for rows in one table that are not contained in another table
- Finally, you can combine all rows from all tables
That looks amazing, doesn’t it? So, with an RDB, you can perform a good number of different kinds of operations.
You might be thinking now that there must be plenty of rules to follow if you want to create a relational DB. There are not so many of them and most of them are logical:
- It doesn’t matter in which order you arrange the initial instances and attributes. For instance, if you make a database of clients, it is not important what you put first: a name or an address.
- Every initial instance should be unique.
- Each table cell is destined for one value only.
- An attribute is given to the values of the same domain. For instance, if an attribute is used for an address indication, you will not put there a currency name.
- Table names in the entire database should be unique.
Types of Databases and Their Application
The relational database model is very popular in different kinds of applications. When it comes to the choice between a relational and non-relational database, most specialists prefer a relational one. These businesses are known for using such kind of databases:
However, if your work is connected with big volumes of distributed data, you should give the preference to a NoSQL database. Such kind of databases supports many data formats, which are not supported by a typical relational database. The main advantage of this database kind is that it can keep unstructured or semi-structured data. But it requires more time and efforts to process it.
These databases are used in social media, for analytics software – everywhere where the user has to handle different data formats.
A typical graph database is one more kind of NoSQL databases. Here, nodes and edges are used to show and discover the relations between data. The main difference from a usual relational database is in the fact, that a graph database shows relations directly. They are explicit, while in a relational database, they are implicit. A graph database is more complex than a usual relational database and allows more complex applications. For example, it can be used for fraud detection.
Advantages of Relational Databases
So, what should you select: a relational or a NoSQL database? What are relational databases applications that provide you with more advantages? All depends on which data you work with. It is a non-structured or a semi-structured data, a NoSQL database is a better choice.
However, if your main domain is connected with structured data, your choice should be a SQL or a relational database. In the second case, you get a number of advantages if you select a relational or a SQL database:
- You perform data storing as well as arrangement based on categories
- It is possible to perform data query in a database
- You can filter the data based on some criteria
- You can add or remove data without any structure modifications
Both SQL and NoSQL databases offer their advantages and have their disadvantages. All depends on the kind of a business you run and the type of data you work with.