Cursor & Trigger in DBMS

When handling databases, there are times we need to process records one at a time (using Cursors) or automatically respond to specific events (using Triggers).

In this guide, we’ll:
✅ Create a Cursor to fetch employees earning more than 50,000
✅ Implement an AFTER-INSERT Trigger to maintain a student audit log

🔹 Cursor

A cursor acts as a pointer that allows processing query results row by row instead of all together. This is especially useful when applying custom logic to individual records.

Step 1: Employee Cursor Example

Let’s create a cursor to list employees with a salary above 50,000.

Step i: Create Employee Table

CREATE TABLE Employees (
Emp_ID NUMBER PRIMARY KEY,
Emp_Name VARCHAR2(50),
Salary NUMBER
);

Step ii: Insert Sample Data

INSERT INTO Employees (Emp_ID, Emp_Name, Salary) VALUES (1, 'Renner', 60000);
INSERT INTO Employees (Emp_ID, Emp_Name, Salary) VALUES (2, 'Samuel', 45000);
INSERT INTO Employees (Emp_ID, Emp_Name, Salary) VALUES (3, 'Ana', 75000);
INSERT INTO Employees (Emp_ID, Emp_Name, Salary) VALUES (4, 'Kylie', 50000);

Step iii: Cursor Implementation

DECLARE
CURSOR emp_cursor IS
SELECT Emp_Name, Salary FROM Employees WHERE Salary > 50000;
v_EmpName Employees.Emp_Name%TYPE;
v_Salary Employees.Salary%TYPE;
BEGIN
OPEN emp_cursor;
LOOP
FETCH emp_cursor INTO v_EmpName, v_Salary;
EXIT WHEN emp_cursor%NOTFOUND;
DBMS_OUTPUT.PUT_LINE('Employee: ' || v_EmpName || ', Salary: ₹' || v_Salary);
END LOOP;
CLOSE emp_cursor;
END;
/
🔹 Trigger

A trigger is a stored procedure that runs automatically when a defined event occurs (INSERT, UPDATE, or DELETE).

Step 2: AFTER INSERT Trigger

We’ll create a Students table and a Students_Audit table to log new registrations.

Step i: Create Students Table

CREATE TABLE Students2 (
Student_ID NUMBER PRIMARY KEY,
Student_Name VARCHAR2(50),
Course VARCHAR2(50)
);

Step ii: Create Students_Audit Table

CREATE TABLE Students_Audit (
Audit_ID NUMBER GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
Student_ID NUMBER,
Student_Name VARCHAR2(50),
Action VARCHAR2(50),
Action_Time TIMESTAMP
);

Step iii: Create AFTER INSERT Trigger

CREATE OR REPLACE TRIGGER trg_after_student_insert
AFTER INSERT ON Students2
FOR EACH ROW
BEGIN
INSERT INTO Students_Audit (Student_ID, Student_Name, Action, Action_Time)
VALUES (:NEW.Student_ID, :NEW.Student_Name, 'INSERT', SYSTIMESTAMP);
END;
/
Step iv: Test the Trigger

INSERT INTO Students2 (Student_ID, Student_Name, Course) VALUES (1, 'Renner', 'Computer Science');
INSERT INTO Students2 (Student_ID, Student_Name, Course) VALUES (2, 'Martin', 'Mechanical Engineering');

Step v: Verify Audit Table

SELECT * FROM Students_Audit;

Conclusion

In this tutorial, we explored:

Cursor → Process query results row by row
Trigger → Automatically log student registrations after insertion

These tools bring efficiency and automation to your SQL workflows!

A special thanks to @santhoshnc Sir for the guidance and support in completing this DBMS assignment successfully.