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:
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