What is Semi Join?
Semi-Join matches the rows of two relations and then show the matching rows of the relation whose name is mentioned to the left side of ⋉ Semi Join operator. I am describing the more details in the below examples. Hopefully, it will help you to understand the semi-join.
Example 1 of Semi Join:
| ID |
Rank |
Salary |
| 101 |
Assistant Professor |
80,000 |
| 102 |
Associate Professor |
90,000 |
| 103 |
Lecturer |
70,000 |
Table 1: Teacher
| ID |
RollNo |
Marks |
| 103 |
2017 – 01 |
80 |
| 104 |
2017 – 02 |
90 |
| 105 |
2017 – 03 |
70 |
Table 2: Student
| ID |
RollNo |
Marks |
| 103 |
2017 – 01 |
80 |
Table 3: Student ⋉ Teacher OR Student Semi Join Teacher
| ID |
Rank |
Salary |
| 103 |
Lecturer |
70,000 |
Table 4: Teacher ⋉ Student OR Teacher SEMI-JOIN Student
Example 2 of Semi Join:
| ID |
Rank |
Salary |
| 101 |
Assistant Professor |
80,000 |
| 102 |
Associate Professor |
90,000 |
| 103 |
Lecturer |
70,000 |
Table 5: Teacher
| ID |
RollNo |
Marks |
| 101 |
2017 – 01 |
80 |
| 103 |
2017 – 02 |
90 |
| 106 |
2017 – 03 |
70 |
Table 6: Student
| ID |
RollNo |
Marks |
| 101 |
2017 – 01 |
80 |
| 103 |
2017 – 02 |
90 |
Table 7: Student ⋉ Teacher OR Student SEMI-JOIN Teacher:
| ID |
Rank |
Salary |
| 101 |
Assistant Professor |
80,000 |
| 103 |
Lecturer |
70,000 |
Table 8: Teacher ⋉ Student OR Teacher SEMI-JOIN Student
Example 3 of Semi Join:
| Employee |
| Name |
EmpId |
DeptName |
| Sameed |
1 |
CS |
| Shahzeb |
2 |
SE |
| Abid |
3 |
CS |
| Shamil |
4 |
IT |
|
| Department |
| DeptName |
Manager |
| SE |
Shahzeb |
| IT |
Shamil |
|
| Employee ⋉ Dept |
| Name |
EmpId |
DeptName |
| Shahzeb |
2 |
SE |
| Shamil |
4 |
IT |
|
