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.
Syntax
Here is the syntax for an INNER JOIN:
INNER JOIN Syntax
SELECT columns
FROM table1
INNER JOIN table2
ON table1.column = table2.column;
ONdefines how the two tables are linked.- The result only includes rows with matching keys in both tables.
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 since they have no enrollments. The enrollment for
student_id = 6is also excluded, as there is no matching student.
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.
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