LEFT JOIN
A LEFT JOIN returns all rows from the left table, and the matching rows from the right table.
If there is no match, the result will contain NULL for columns from the right table.
Syntax
Here is the syntax for a LEFT JOIN:
LEFT JOIN Syntax
SELECT columns
FROM table1
LEFT JOIN table2
ON table1.column = table2.column;
- The left table is listed first (
table1). - All rows from the left table are included, even if there is no match in the right table.
Example: Students and Enrollments
Below is an example of a LEFT JOIN between the students and enrollments tables.
students
| student_id | name |
|---|---|
| 1 | John Miller |
| 2 | Lisa Brown |
| 3 | David Smith |
| 4 | Emily Davis |
| 5 | Michael Jones |
enrollments
| student_id | class_name |
|---|---|
| 1 | Math |
| 1 | Science |
| 2 | History |
| 5 | Art |
LEFT JOIN example
SELECT students.name, enrollments.class_name
FROM students
LEFT JOIN enrollments
ON students.student_id = enrollments.student_id;
Result:
| name | class_name |
|---|---|
| John Miller | Math |
| John Miller | Science |
| Lisa Brown | History |
| David Smith | NULL |
| Emily Davis | NULL |
| Michael Jones | Art |
David Smith and Emily Davis appear even though they have no enrollments.
When do I use LEFT JOIN?
LEFT JOIN is useful when:
- You want to include all entries from the left table
- You need to identify unmatched records
- You're generating full lists (e.g. all customers with or without purchases)
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