CURSOR AND TRIGGER

A cursor in a Database Management System (DBMS) is a special control structure that enables traversal over the records in a result set obtained by executing a query. Unlike traditional SQL statements that operate on the entire set of rows simultaneously, a cursor allows row-by-row retrieval and processing of data. This makes it particularly useful when fine-grained, sequential manipulation of query results is required, such as performing conditional checks, applying calculations, or handling complex business logic on each individual row.

CREATE TABLE Employee (
EmpID INT PRIMARY KEY,
EmpName VARCHAR(50),
Salary INT
);

INSERT INTO Employee VALUES
(1, 'Arjun', 45000),
(2, 'Priya', 60000),
(3, 'Kiran', 75000),
(4, 'Meera', 48000),
(5, 'Rahul', 90000);

OUTPUT

Cursor Code (Employees with Salary > 50,000)
DECLARE
CURSOR high_salary_cursor IS
SELECT EmpName FROM Employee WHERE Salary > 50000;
v_name Employee.EmpName%TYPE;
BEGIN
OPEN high_salary_cursor;
LOOP
FETCH high_salary_cursor INTO v_name;
EXIT WHEN high_salary_cursor%NOTFOUND;
DBMS_OUTPUT.PUT_LINE('Employee: ' || v_name);
END LOOP;
CLOSE high_salary_cursor;
END;

Trigger Example (AFTER INSERT Trigger)
Create Student and Audit Tables
CREATE TABLE Studt (
StudentID VARCHAR(10) PRIMARY KEY,
StudentName VARCHAR(50)
);

CREATE TABLE Student_Audit (
AuditID INT GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
StudentID VARCHAR(10),
StudentName VARCHAR(50),
ActionDate TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);

Create AFTER INSERT Trigger
CREATE OR REPLACE TRIGGER student_insert_audit
AFTER INSERT ON Students
FOR EACH ROW
BEGIN
INSERT INTO Student_Audit (StudentID, StudentName)
VALUES (:NEW.StudentID, :NEW.StudentName);
END;

Insert Data into Studt
INSERT INTO Students VALUES ('S01', 'Arjun');
INSERT INTO Students VALUES ('S02', 'Priya');
INSERT INTO Students VALUES ('S03', 'Kiran');

SELECT * FROM Student_Audit;