SQL Basics Overview

SQL (Structured Query Language) is the standard language for interacting with relational databases. Whether you are building an app or analyzing data, mastering SQL basics is the first step.

Why SQL Basics Matter

Every complex query is built from these simple blocks:

1. SELECT: Fetching specific data.
2. WHERE: Filtering records based on conditions.
3. GROUP BY: Summarizing data into categories.
4. Constraints: Ensuring data integrity.

In this module, we will cover everything from simple selection to complex grouping and data validation.

Module Roadmap

Topic	Key Skill	Interview Weight
SELECT & Aliases	Fetching + renaming columns	High
WHERE & Operators	Filtering with conditions	High
ORDER BY & Pagination	Sorting + LIMIT/OFFSET	Medium
GROUP BY & Aggregates	Summarizing with COUNT/SUM/AVG	Very High
Constraints & Keys	PRIMARY KEY, FOREIGN KEY, UNIQUE	High
DDL & DML	CREATE, ALTER, INSERT, UPDATE, DELETE	Medium
Built-in Functions	String, Date, Math, NULL handling	Medium

SQL Statement Categories

SQL statements fall into five main categories:

• DDL (Data Definition Language): CREATE, ALTER, DROP — define database structure.
• DML (Data Manipulation Language): SELECT, INSERT, UPDATE, DELETE — manage data.
• DCL (Data Control Language): GRANT, REVOKE — control permissions.
• TCL (Transaction Control Language): COMMIT, ROLLBACK, SAVEPOINT — manage transactions.
• DQL (Data Query Language): SELECT — query data (often grouped under DML).

Understanding these categories helps you speak the same language as interviewers and database administrators.

Execution Order (Logical)

SQL queries are written in a certain order but executed in a different one. Knowing this order is critical for debugging and optimisation:

1. FROM / JOIN — identify source tables
2. WHERE — filter rows
3. GROUP BY — group rows
4. HAVING — filter groups
5. SELECT — pick columns
6. DISTINCT — remove duplicates
7. ORDER BY — sort
8. LIMIT / OFFSET — paginate

Prerequisites for This Module

You should be comfortable with basic programming concepts like variables, conditions, and loops. No prior SQL experience is required — we start from the ground up.