Free Handbook - What you need to know about relational database management systems

_Introducing RDBMS - Relational Database Management System. Read more to learn about the basis for SQL.
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By Gonçalo Calvinho, Role — Feb 04, 2022 — 15 min. — Databases, Best Practices, Free Guides

What is SQL?

Standard computer language for Relational Database Systems. It’s used to store, manipulate and retrieve data in a relational database.

It allows users to access and manipulate data, create or destroy database objects and set user permissions.

SQL Commands

The standard SQL commands used to interact with the database are classified into 3 distinct categories (DDL, DML and DCL)

DDL – Data Definition Language

DML – Data Manipulation Language

DCL – Data Control Language

GRANT | Assings privileges to users |
REVOKE | Removes granted privileges |
Constraints

Constraints are the rules enforced on data columns on a table. These are used to limit the type of data that can be inserted into a column, ensuring the accuracy and reliability of the data in the database.

Some of the most commonly used constraints in SQL are:

NOT NULL – Ensures that a column cannot have a NULL value
UNIQUE – Ensures that all the values in a column are different
PRIMARY KEY – Refers to a primary key in another table. Links both table’s data and prevents errors.
FOREIGN KEY – Uniquely identifies a row in another table
CHECK – Ensures that all values in a column satisfy certain criteria
INDEX – Used to create and retrieve data from the database very quickly

RDBMS

RDBMS stands for Relational Database Management System, and is the basis for SQL. It’s a database management system that is based on the relational model (all the data is related to each other ).

The data in a RDBMS is stored in database objects called tables. A table is basically a collection of related data, consisting of columns and rows.

A column is a field in a table designed to maintain specific information about every record in the table.

A row is an individual record of data in a table. It is a collection of attributes.

Designing a database: Best Practices

Consider every viewpoint
Don’t start building a database without input from the project owner and stakeholders.
Get consensus on precise expectations/functionality

Choose a database type
Usually as easy as deciding between SQL and NoSQL
Depending on the project there are types of databases more appropriate, e.g., Oracle for large organizations with structured data, SQL Server for error handling or XML/JSON integrations and NoSQL for machine learning and IoT applications

Normalize data
Data normalization is critical to achieve minimum redundancy and data consistency
When a database abides by the first three normal forms we can say it’s normalized

Transparency
Design with the end users in mind
Use consistent naming conventions, as to make things easy for those who may need to modify the database in the future

Define constraints
This is important to maintain data integrity and enforce business rules
This way the database will prevent bad data from getting in

Document everything
Documentation is essential, although sometimes annoying, promotes a clean development and makes maintenance easy
Document the design, implementation and every database object for future users

Keep privacy primary
In the era of GDPR privacy concerns are increasingly important
Encrypt passwords and be careful when assigning administrator permissions
Vulnerabilities impact data integrity, which impacts everything else

Optimize for speed
Create indexes for queries that are used regularly
Use an analysis tool to check if an index or clustered index is necessary

Avoid dynamic SQL
Always avoid dynamic queries, as this type of development can lead to SQL injection attacks.

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