INNER JOIN
An INNER JOIN returns rows where both tables have matching values in the joined column.
It's the most commonly used join in SQL.
Syntax
Here is the syntax for a INNER JOIN:
INNER JOIN Syntax
SELECT columns
FROM table1
INNER JOIN table2
ON table1.column = table2.column;
ONdefines how the two tables are linked.- Only rows with matching keys in both tables will be returned.
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 |
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 because they have no enrollments. The enrollment for
student_id = 6is also excluded because there is no matching student.
When do I use INNER JOIN?
Use INNER JOIN when you:
- Need to connect related rows between tables
- Want only the rows where both sides match
- Build reports that rely on cross-referenced data
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