Implicit Join and Explicit Join are two ways to combine data from multiple tables in SQL. The main difference is how the relationship between the tables is specified.
- Implicit Join combines tables by listing them in the FROM clause and specifying the join condition in the WHERE clause.
- Explicit Join uses the JOIN keyword to specify how the tables should be combined.
Difference Between Implicit Join & Explicit Join
The table below shows the major differences between Implicit Join and Explicit Join:
| Implicit Join | Explicit Join |
|---|---|
| Tables are listed together in the FROM clause. | Tables are joined using the JOIN keyword. |
| The join condition is specified in the WHERE clause. | The join condition is specified using the ON clause. |
| Uses older SQL join syntax. | Uses modern SQL join syntax. |
| Can be less clear when joining multiple tables. | Makes the join relationship clearer. |
| Mainly used for inner joins. | Supports INNER JOIN, LEFT JOIN, RIGHT JOIN and other join types. |
Example of Implicit and Explicit Join
The following examples demonstrate how the same result can be obtained using both Implicit Join and Explicit Join.
Table: employee
| employee_id | name | department_id |
|---|---|---|
| 1 | Alice | 10 |
| 2 | Bob | 20 |
Table: department
| department_id | department_name |
|---|---|
| 10 | HR |
| 20 | Sales |
Implicit Join
Query:
SELECT e.name, d.department_nameFROM employee AS e, department AS dWHERE e.department_id = d.department_id;
Output:
| name | department_name |
|---|---|
| Alice | HR |
| Bob | Sales |
Explicit Join
Query:
SELECT e.name, d.department_nameFROM employee AS eINNER JOIN department AS dON e.department_id = d.department_id;
Output:
| name | department_name |
|---|---|
| Alice | HR |
| Bob | Sales |
Both queries produce the same result, but Explicit Join is generally preferred because the join condition is clearly separated from other filtering conditions.
