? MySQL INNER JOIN

? Quick Overview

The INNER JOIN keyword selects records that have matching values in both tables. It returns only rows where a match exists between the joined tables' columns.

? Key Concepts

Match-only results: INNER JOIN excludes rows without matching counterparts.
Join condition: Use ON to specify the equality between common columns.
Multiple joins: You can chain multiple INNER JOIN clauses to combine several tables.

? Syntax / Theory

? View Code Example

-- Syntax for INNER JOIN
SELECT columns
FROM table1
INNER JOIN table2
ON table1.common_column = table2.common_column;

? Code Example(s)

? View Code Example

-- Get all students and their corresponding courses
SELECT students.name, courses.course_name
FROM students
INNER JOIN courses
ON students.course_id = courses.course_id;

? View Code Example

-- Get all orders and their related customer information
SELECT orders.order_id, customers.customer_name
FROM orders
INNER JOIN customers
ON orders.customer_id = customers.customer_id;

? Live Output / Explanation

How results behave

The queries above will return only rows where the join condition matches. For example, the student-course query returns rows for students who have a course_id that exists in the courses table. Any student without a matching course_id will be excluded.

Use LEFT JOIN if you want to include all rows from the left table even when there is no match on the right table.

✅ Tips & Best Practices

Prefer joining on indexed columns for better performance.
Always qualify columns with table names when joining multiple tables to avoid ambiguity.
Verify join conditions when chaining multiple joins to prevent accidental row multiplication.

? Try It Yourself / Practice Tasks

Write a query to find all students who have enrolled in any course using INNER JOIN.
List all customers and their orders using INNER JOIN between customers and orders.
Join three tables (e.g., orders → customers → products) and ensure correct join conditions to retrieve product names per order.