SQL Joins with Real-Life Examples🔥Inner, Left & Right Join Explained!

Summary

The video explains how SQL joins combine related rows from multiple tables in a single query. The examples use students and courses tables linked by student_id.

Join types

• INNER JOIN: Returns only rows with matching values in both tables. In the example, it shows students enrolled in a course. Students without a course and courses without an enrolled student are excluded.
• LEFT JOIN: Returns every row from the table named after FROM, along with matching rows from the joined table. If there is no match, the joined table’s columns contain NULL. This is useful for finding all students, including those who have not enrolled in a course.
• RIGHT JOIN: Returns every row from the table named after RIGHT JOIN, along with matching rows from the table named after FROM. Unmatched columns contain NULL. This is useful for listing all courses, including courses with no enrolled students.

A RIGHT JOIN can be rewritten as a LEFT JOIN by swapping the table order. The examples show how to retrieve all courses using either a RIGHT JOIN or a LEFT JOIN with courses first.

Practical walkthrough

The tutorial demonstrates the process in MySQL Workbench:

1. Create a database and students and courses tables.
2. Add student and course details, using student_id to connect the tables.
3. Use an ON condition such as students.student_id = courses.student_id.
4. Select specific, table-qualified columns—such as the student ID, student name, and course name—to avoid ambiguity and return only the needed data.

A final real-world example previews using a join in an email-verification workflow. It matches data from a verification-token table with a user table to retrieve an email in one query rather than querying each table separately.

Main speaker/source: The video’s presenter from Thapa Technical, who identifies himself as Codifier.