diff --git a/03_Joins/README.md b/03_Joins/README.md index 08c3007..8e627e7 100644 --- a/03_Joins/README.md +++ b/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) |