Why does a SELECT INTO sql statement give me an error in this Pl/SQL Function?

Question

I am trying to create a pl/sql function to calculate the total of all salaries in an employee table and return it. I am using the sum function but i am getting an error

I have tried changing the sql statement to this solution provided a stack overflow

SELECT (select sum(salary) from employee) INTO total_sum FROM dual;

Below is a sum statement working

SQL> select sum(salary) from employee;

SUM(SALARY)
-----------
281000

Here is the Pl/SQL Function

CREATE OR REPLACE FUNCTION total_salary(dep_number IN NUMBER)
RETURN NUMBER
IS
total_sum NUMBER;
BEGIN
SELECT (select total_sum sum(salary) from employee) INTO total_sum FROM     dual;
return total_sum;
END total_salary;

Here is the error Warning: Function created with compilation errors.

SQL> show errors
Errors for FUNCTION TOTAL_SALARY:

LINE/COL ERROR
-------- -----------------------------------------------------------------
6/1      PL/SQL: SQL Statement ignored
6/29     PL/SQL: ORA-00923: FROM keyword not found where expected

I expect the function to return the sum of the salary

Answer 1

Try this:

CREATE OR REPLACE FUNCTION total_salary(dep_number IN NUMBER) 
   RETURN NUMBER 
   IS total_sum NUMBER;
   BEGIN 
      SELECT SUM(salary) 
      INTO total_number 
      FROM employee
      WHERE deptid = dep_number; 
      RETURN(total_sum); 
    END;