Definition of cursor in DBMS:
A cursor in DBMS is a database object used to retrieve, manipulate, and navigate through a result set row by row.
It acts like a pointer that allows you to process individual rows returned by an SQL query.
Example – Retrieving and Displaying Employee Records Where the Salary is Greater Than ₹50,000
Step 1: Create Employee Table
CREATE TABLE Employee (
Emp_ID NUMBER PRIMARY KEY,
Emp_Name VARCHAR2(50),
Salary NUMBER
);
Step 2: Insert Sample Data
INSERT INTO Employee (Emp_ID, Emp_Name, Salary) VALUES (1, 'Ramesh', 60000);
INSERT INTO Employee (Emp_ID, Emp_Name, Salary) VALUES (2, 'Suresh', 45000);
INSERT INTO Employee (Emp_ID, Emp_Name, Salary) VALUES (3, 'Anita', 75000);
INSERT INTO Employee (Emp_ID, Emp_Name, Salary) VALUES (4, 'Kavya', 50000);
Step 3: Create and Process Cursor
DECLARE
CURSOR emp_cursor IS
SELECT Emp_Name, Salary FROM Employee WHERE Salary > 50000;
v_EmpName Employee.Emp_Name%TYPE;
v_Salary Employee.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;
Explanation:
The cursor emp_cursor selects employees earning more than 50,000.
DBMS_OUTPUT.PUT_LINE prints each employee’s name and salary.
Defintion of trigger in DBMS:
A trigger is a stored procedure that automatically executes (fires) in response to certain events on a table such as INSERT, UPDATE, or DELETE.
Example – Executing an AFTER INSERT Operation on the Students Table
Step 1: Create Students Table
CREATE TABLE Students (
Student_ID NUMBER PRIMARY KEY,
Student_Name VARCHAR2(50),
Course VARCHAR2(50)
);
Step 2: Create Student_Audit Table
CREATE TABLE Student_Audit (
Audit_ID NUMBER GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
Student_ID NUMBER,
Student_Name VARCHAR2(50),
Action VARCHAR2(50),
Action_Time TIMESTAMP
);
Step 3: Create AFTER INSERT Trigger
CREATE OR REPLACE TRIGGER trg_after_student_insert
AFTER INSERT ON Students
FOR EACH ROW
BEGIN
INSERT INTO Student_Audit (Student_ID, Student_Name, Action, Action_Time)
VALUES (:NEW.Student_ID, :NEW.Student_Name, 'INSERT', SYSTIMESTAMP);
END;
Explanation:
Trigger automatically logs new students into Student_Audit.
NEW references the inserted row, and SYSTIMESTAMP captures insertion time.
Step 4: Test Trigger
INSERT INTO Students (Student_ID, Student_Name, Course) VALUES (1, 'Ravi', 'Computer Science');
INSERT INTO Students (Student_ID, Student_Name, Course) VALUES (2, 'Meena', 'Electrical Engineering');
Step 5: Verify Audit Table
SELECT * FROM Student_Audit;
Conclusion:
*Cursors help in row-by-row processing of query results when set-based operations are not sufficient.
*Triggers automate database tasks by responding to data modification events automatically.
*Both cursors and triggers enhance database functionality, control, and automation but should be used carefully to maintain performance and data integrity.
Thank @santhoshnc Sir for his valuable guidance and continuous support in successfully completing this DBMS assignment.
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