Blog Posts

Introduction to SQL

March 7, 2025 | Categories: Intro

Welcome to the SQL Playground. This space allows for learning SQL through exercises, coding challenges, and hands-on practice.

What is SQL?

SQL (Structured Query Language) is a powerful language used to interact with relational databases. Whether you are a beginner or an experienced developer, SQL is an essential skill for …

SQL Lesson 1: SELECT statement

March 27, 2025 | Categories: Information

To retrieve data from a SQL database, we use SELECT statements, which are commonly referred to as queries. A query is simply a request that tells the database what data we need, where to find it, and optionally, how to process it before returning the results. Queries follow a specific …

Tables

April 2, 2025 | Categories: Information

✅ Tables are the main structures in the relational database. Each table always represents a single specific subject. The logical order of rows and columns within the table is of absolutely no importance. Every table contains at least one column, known as a primary key, that uniquely identifies each of its …

SQL Lesson 2: Queries with constraints

April 3, 2025 | Categories: Information

In the previous lesson, we explored how to retrieve data using the SELECT statement. Now it’s time to make our queries smarter by filtering the data to return only the rows we’re interested in. This is where the WHERE clause comes into play.

Imagine you’re working with a large dataset …

Relationships

April 4, 2025 | Categories: Information

If rows in a given table can be associated in some way with rows in another table, the tables are said to have a relationship between them. The manner in which the relationship is established depends on the type of relationship. Three types of relationships can exist between a pair …

SQL Lesson 3: Filtering and Sorting Query Results

April 22, 2025 | Categories: Information

In previous lessons, we learned how to retrieve data from a database using the SELECT statement and apply conditions using WHERE. Now, let’s dive into more ways to refine your query results by:

  • Eliminating duplicate rows

  • Sorting data in a meaningful order

  • Returning just a portion of the results …

SQL Lesson 4: Review & Practice – Crafting Real-World SELECT Queries

May 13, 2025 | Categories: Information

You've built a strong foundation with the basics of SQL:

  • Retrieving data using SELECT

  • Filtering results using WHERE

  • Removing duplicates with DISTINCT

  • Sorting with ORDER BY

  • Limiting results with LIMIT and OFFSET

Now it’s time to take a step back, review what you’ve learned, and apply your knowledge to practical …

SQL Lesson 5: INNER JOIN - Combining Data from Multiple Tables

June 19, 2025 | Categories: Information

So far, we've been working with single tables to retrieve, filter, and sort data. But in real-world databases, information is often split across multiple related tables. This is where the power of SQL really begins to shine!

Imagine you're building a library system. Instead of storing all book information in …

SQL Lesson 6: OUTER JOINs - Finding All Records

June 25, 2025 | Categories: Information

In Lesson 5, we learned how to use INNER JOINs to combine data from multiple tables. INNER JOIN only returns records when there is a match in both tables. But what if you want to see ALL records from one table, even when there's no match in the other …