Inner Join = Equi Join = Natural Join is the usually same.
SELECT * FROM employee
INNER JOIN department
ON employee.D_id = department.D_id
SELECT * FROM employee, department
WHERE employee.D_id = department.D_id
Inner join result :
An inner join has an ON clause that specifies the join conditions. Rather than having a huge rowset in memory and filtering the data, this join extracts only the data that meets the join conditions. The keyword INNER is optional because a JOIN clause will be INNER by default. An inner join is called equi-join when all the columns are selected with a *, or natural join otherwise.
inner or natural joins - just a "regular" join.
| Employee table: | |
|---|---|
| LN | D_Id |
| Kamal | 31 |
| Jones | 33 |
| Singh | 33 |
| Smith | 34 |
| Robinson | 34 |
| Jasper | 36 |
| Department Table: | |
|---|---|
| Department Name | D_Id |
| Sales | 31 |
| Engineering | 33 |
| Clerical | 34 |
| Marketing | 35 |
Example inner join (ANSI 92 standard syntax):
SELECT * FROM employee
INNER JOIN department
ON employee.D_id = department.D_id
Example inner join (non-standard syntax):
SELECT * FROM employee, department
WHERE employee.D_id = department.D_id
Inner join result :
| LN | D_Id | Department Name | D_Id |
| Smith | 34 | Clerical | 34 |
| Jones | 33 | Engineering | 33 |
| Robinson | 34 | Clerical | 34 |
| Singh | 33 | Engineering | 33 |
| Kamal | 31 | Sales | 31 |