Semi-Join with Examples in Relational Algebra (Database Systems)

Today, in this fresh and new article, we will cover the following topics;

1. What is Semi Join?
2. Examples of Semi Join

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

 

Topic Covered

Semi-Join with Examples in Relational Algebra, Database Systems.