pl/sql SQL Statement ignored and missing right parenthesis - oracle

Question

this code has to sum salary of employees of department_id 100.so it gives this error "missing right parenthesis"
DECLARE
v_department_name VARCHAR(100);
v_department_manager VARCHAR(100);
v_totalsalary NUMBER(30);
BEGIN
SELECT departments.department_name, concat(employees.first_name,
employees.last_name), employees.salary INTO v_department_name,
v_department_manager, v_totalsalary
FROM employees JOIN departments ON employees.department_id =
departments.department_id
WHERE employees.salary = (SELECT departments.department_id,
sum(employees.salary)
FROM EMPLOYEES
where departments.department_id=100
GROUP BY DEPARTMENT_ID
ORDER BY DEPARTMENT_ID);
DBMS_OUTPUT.PUT_LINE ('Department Name is : ' || v_department_name || 'And
Department Manager is : ' || v_department_manager || 'Total Amount of Salary
is : ' || v_totalsalary );
END;

Answer 1

The "missing right parenthesis" error is clearly caused by the ORDER BY clause in the subquery (where it is not allowed).
Once you clear that error, you get the "too many values" error, because you are comparing a single variable (salary) to the output from a subquery that returns two values (department_id AND sum(salary)). Not sure why you thought you need to include the department_id in the SELECT clause of the subquery.
When you include error messages in your question, include the full text of the message (which shows the line number and position at which the error occurred - a crucial detail!)
Take it one small step at a time. Forget for the moment PL/SQL; are you able to write the correct query in SQL, which will return the department name, the manager's name and the sum of the salaries of all the employees in the department? If you can do that, then the PL/SQL around it is easy.
Here is one way to get all the values in one SQL statement:
select d.department_name,
m.first_name || ' ' || m.last_name as manager_name,
sum(e.salary) as sum_salary
from departments d
join
employees m on d.manager_id = m.employee_id
join
employees e on d.department_id = e.department_id
where d.department_id = 100
group by d.department_id, d.department_name, m.first_name, m.last_name
;
DEPARTMENT_NAME MANAGER_NAME SUM_SALARY
--------------- --------------- ----------
Finance Nancy Greenberg 51608
Perhaps 80% of writing good PL/SQL code is simply writing good, efficient SQL statements. If you have any difficulty with this query, you should probably spend the majority of your time writing SQL statements, for the next few days or weeks; return to PL/SQL when you feel this query (in my answer) is "simple", "easy", "standard" (which it is!)