Revise README for SQL Joins module

03_Joins/README.md

@@ -1,61 +1,55 @@
-# SQL Joins
-
-## Overview
-
-SQL Joins are used to combine data from multiple tables using a related column.
-
-In real-world analytics, data is rarely stored in a single table. Joins allow analysts to connect datasets and answer business questions.
-
+# 03 — SQL Joins
+
+> **Module 3 of the SQL Engineering Handbook**
+> Real-world data never lives in one table. This module teaches you to connect it.
+
+[![Level](https://img.shields.io/badge/Level-Beginner%20%E2%86%92%20Intermediate-yellow)]()
+[![Estimated Time](https://img.shields.io/badge/Time-3--4%20hrs-blue)]()
+[![Topics](https://img.shields.io/badge/Topics-5-orange)]()
+[![Interview Critical](https://img.shields.io/badge/Interview-Critical-red)]()
+[![Status](https://img.shields.io/badge/Status-Complete-success)]()
+
 ---
-
-## Topics Covered
-
-### Beginner
-
-- INNER JOIN
-- LEFT JOIN
-- RIGHT JOIN
-
-### Intermediate
-
-- SELF JOIN
-
----
-
-## Schema Used
-
-employees
-    │
-    ▼
-departments
-    │
-    ▼
-locations
-
+
+## 📑 Table of Contents
+
+- [Overview](#-overview)
+- [Topics Covered](#-topics-covered)
+- [Folder Structure](#-folder-structure)
+- [Recommended Learning Order](#-recommended-learning-order)
+- [Schema Used](#-schema-used)
+- [How Joins Actually Work](how-joins-actually-work)
+- [Skills Developed](#-skills-developed)
+- [Business Applications](#-business-applications)
+- [Interview Importance](#-interview-importance)
+- [Best Practices](#-best-practices)
+- [Prerequisites](#-prerequisites)
+- [How to Use This Module](#-how-to-use-this-module)
+- [Next Section](#-next-section)
 ---
-
-## Business Applications
-
-- Employee reporting
-- Department analysis
-- Workforce planning
-- Location-based analytics
-- Manager hierarchy analysis
-
+ 
+## 🔎 Overview
+ 
+SQL **joins** are used to combine data from multiple tables using a related column.
+ 
+In real-world systems, data is normalized and spread across many tables — employees in one table, departments in another, locations in a third. Joins are what let you reconnect that data and ask questions that span across it, like *"which employees work in which locations, under which managers?"*
+ 
+This is the module where SQL stops being about *one table* and starts being about *your entire database*.
+ 
 ---
-
-## Skills Developed
-
-- Combining tables
-- Understanding relationships
-- Foreign key usage
-- Multi-table querying
-- Hierarchical analysis
-
----
-
-## Interview Importance
-
-Joins are among the most frequently asked SQL interview topics.
-
-A strong understanding of joins is essential for Data Analyst and Data Scientist roles.
+ 
+## 📖 Topics Covered
+ 
+### Beginner
+ 
+| No. | Topic | Description | Files |
+|----|-------|--------------|-------|
+| 01 | **INNER JOIN** | Return only matching rows from both tables | [`01_INNER_JOIN.md`](./01_INNER_JOIN.md) · [`01_INNER_JOIN.sql`](./01_INNER_JOIN.sql) |
+| 02 | **LEFT JOIN** | Return all rows from the left table, matched or not | [`02_LEFT_JOIN.md`](./02_LEFT_JOIN.md) · [`02_LEFT_JOIN.sql`](./02_LEFT_JOIN.sql) |
+| 03 | **RIGHT JOIN** | Return all rows from the right table, matched or not | [`03_RIGHT_JOIN.md`](./03_RIGHT_JOIN.md) · [`03_RIGHT_JOIN.sql`](./03_RIGHT_JOIN.sql) |
+ 
+### Intermediate
+ 
+| No. | Topic | Description | Files |
+|----|-------|--------------|-------|
+| 04 | **SELF JOIN** | Join a table to itself — used for hierarchies | [`04_SELF_JOIN.md`](./04_SELF_JOIN.md) · [`04_SELF_JOIN.sql`](./04_SELF_JOIN.sql) |