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Jessica Aki
Jessica Aki

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Databases & SQL Basics As A Beginner: A Practical Introduction

#database #sql #beginners #postgressql

Databases & SQL Basics: What I Learned on Day One

Today I officially started my journey into databases and SQL. Instead of rushing into complex queries, I focused on understanding what databases actually are, how they’re managed, and how SQL is used to interact with them.

This post captures what I learned on my first day, both the concepts and the practical SQL skills.

What Is a Database?

A database is a structured collection of related data stored and organized so it can be easily accessed, managed, and updated. Databases are used everywhere, by individuals, businesses, and governments.

They can be as large and complex as a national citizens’ database, or as simple as a friends list, an invoice table, or a sales record.

To manage databases digitally, we use Database Management Systems (DBMS).

What Is a DBMS?

A DBMS is software that allows users to store, manage, and maintain databases efficiently and securely. Examples are PostgreSQL, MySQL, MariaDB, Oracle Database, MongoDB, Firebase, Supabase, Redis, couchDB and lots more.

A DBMS is a medium that provides:

  • Data storage and organization
  • Security through access control
  • Backup and recovery
  • Easy import and export of data
  • Support for CRUD operations: Create, Read (Retrieve), Update and Delete on data

Types of Databases

Databases generally fall into two broad categories:

Relational Databases (SQL)

Relational databases store data in tables made up of rows and columns. The data is structured, and relationships between tables are clearly defined. They use SQL (Structured Query Language) to perform CRUD operations.

Examples are PostgreSQL, MySQL, MariaDB, Oracle Database and more.

Non-Relational Databases (NoSQL)

Non-relational databases store data in formats that aren’t traditional tables. They don’t use SQL, but instead rely on database-specific query languages or APIs. These can include:

  • Key-value pairs
  • Documents (JSON, XML)
  • Graphs
  • Blobs Examples are MongoDB, Firebase Firestore, Cassandra, Redis and more.

Understanding Keys in Databases

One of the most important concepts I learned today was keys. Keys are attributes used to uniquely identify records in a table and to define relationships between tables.

  • Primary Key
    A unique identifier for each record in a table.

  • Natural Keys
    Primary keys that map to real-world identifiers, such as: Student ID, National ID, BVN or SSN

  • Surrogate Keys
    Artificially generated keys (like auto-incremented IDs) used when natural keys are impractical.

  • Foreign Keys
    Keys that reference the primary key of another table, creating relationships between tables.

SQL Basics I Learned Today

I practiced SQL using interactive exercises, and here are the key things I learned.

Selecting Data

SELECT * FROM table; -- select all columns from a table
SELECT column1, column2 FROM table; -- select specific columns from a table
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Filtering with WHERE

SELECT * FROM table WHERE field > 9; -- select all columns from a table fulfilling a specified condition
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I also learned to use logical operators like AND and OR to build more complex filters.

Getting Unique Values

SELECT DISTINCT field FROM table;
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Counting Rows

SELECT COUNT(*) FROM table;
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Using Aliases

SELECT field AS Total FROM table;
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Working with Strings

SQL uses single quotes for strings.

SELECT * FROM table WHERE name = 'John';
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Pattern matching with LIKE

SELECT * FROM table WHERE name LIKE 'T%';
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String length and parsing

SELECT * FROM table WHERE LENGTH(name) > 3;
SELECT * FROM table WHERE LEFT(name, 1) = 'T';
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Working with Numbers

Rounding values

SELECT ROUND(value, 2) FROM table;
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Finding even numbers using modulo

SELECT * FROM table WHERE MOD(id, 2) = 0;
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Final Thoughts

What stood out to me today is how powerful even basic SQL queries can be. Simple SELECT statements already allow you to ask meaningful questions about data.

This first day helped me build a strong foundation, and I’m looking forward to creating tables, inserting data, and designing real database structures next.

— Jessica Aki
Data and Database Engineering Enthusiast

I’m documenting my journey into data engineering learning SQL, databases, and the systems behind modern data platforms.

Top comments (1)

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Jedidiah •

Very detailed