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-- View the students table
SELECT * FROM students;

-- View the enrollments table
SELECT * FROM enrollments;

-- Return student names along with their enrolled class
SELECT students.name, enrollments.class_name
FROM students
INNER JOIN enrollments
ON students.student_id = enrollments.student_id;

# INNER JOIN

An `INNER JOIN` returns rows where **both tables contain matching values** in the joined column.  
It is the most commonly used join in SQL.

<br/>

## Syntax

Here is the syntax for an `INNER JOIN`:

```sql title="INNER JOIN Syntax"
SELECT columns
FROM table1
INNER JOIN table2
ON table1.column = table2.column;
```

* `ON` defines how the two tables are linked.
* The result only includes rows with matching keys in both tables.

<br/>

## Example: Students and Enrollments

Below is an example of a `INNER JOIN` between the `students` and `enrollments` tables.

*students*

| student_id | name         |
| ----------- | ------------ |
| 1           | John Smith   |
| 2           | Emily Davis  |
| 3           | Michael Lee  |
| 4           | Jessica Hall |
| 5           | David Miller |

*enrollments*

| student_id | class_name |
| ----------- | ----------- |
| 1           | Math        |
| 1           | History     |
| 2           | Biology     |
| 3           | Chemistry   |
| 6           | Geography   |

```sql title="INNER JOIN example"
SELECT students.name, enrollments.class_name
FROM students
INNER JOIN enrollments
ON students.student_id = enrollments.student_id;
```

### Result:

| name        | class_name |
| ----------- | ----------- |
| John Smith  | Math        |
| John Smith  | History     |
| Emily Davis | Biology     |
| Michael Lee | Chemistry   |

>  Jessica Hall and David Miller are excluded since they have no enrollments.
>  The enrollment for `student_id = 6` is also excluded, as there is no matching student.

<br/>

## When should I use `INNER JOIN`?

Use an `INNER JOIN` when you need to retrieve related records that exist in both tables.
Because it only returns rows found in **both tables**, it is especially useful for creating reports, checking participation, and analyzing linked data.

An INNER JOIN is used to combine rows from two tables based on a related column between them. It only returns the rows where there is a match in both tables, making it one of the most efficient ways to retrieve related data from multiple tables in SQL.

student_id	name
1	John Smith
2	Emily Davis
3	Michael Lee
4	Jessica Hall
5	David Miller

name	class_name
John Smith	Math
John Smith	History
Emily Davis	Biology
Michael Lee	Chemistry

INNER JOIN

Syntax

Example: Students and Enrollments

Result:

When should I use INNER JOIN?

What does an INNER JOIN do in SQL?

When should I use `INNER JOIN`?