Help me in solving PLSQL41 problem

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My issue

Practice - Multiple table udpate
We have an employees table with columns emp_id, emp_name, department and salary.

We also have a department_salary table with columns department and avg_salary.

Task
Write a PLSQL query for a trigger to update the ‘department_salary’ table with average salary for each department whenever insert or update queries are run on employee table.

Update the trigger update_department_salary given in the IDE to get the following output.

Expected output
DEPARTMENT AVG_SALARY

HR 56667
Operations 56000

My code

CREATE OR REPLACE TRIGGER update_department_salary
AFTER INSERT OR UPDATE ON employees
FOR EACH ROW
DECLARE
    v_avg_salary NUMBER;
BEGIN
    -- Calculate the average salary for each department and update the department_salary table
    FOR dept_rec IN (SELECT DISTINCT department FROM employees) LOOP
        -- Calculate the average salary for the department
        SELECT AVG(salary)
        INTO v_avg_salary
        FROM employees
        WHERE department = dept_rec.department;

        -- Update the department_salary table with the calculated average salary
        MERGE INTO department_salary ds
        USING (SELECT dept_rec.department AS department FROM dual) d
        ON (ds.department = d.department)
        WHEN MATCHED THEN
            UPDATE SET ds.avg_salary = v_avg_salary
        WHEN NOT MATCHED THEN
            INSERT (department, avg_salary) VALUES (dept_rec.department, v_avg_salary);
    END LOOP;
END;
/
SELECT * FROM department_salary;

Learning course: Database management systems
Problem Link: Practice - Multiple table udpate in Database management systems