I want to Create a function that returns the number of employees in a department - sql

Question

The query I tried is this,
CREATE OR REPLACE FUNCTION get_dno (d_no IN Employee.DepartmentNo%TYPE)
RETURN NUMBER
IS
d_cnt NUMBER;
BEGIN
SELECT COUNT(*) INTO d_cnt
FROM employee GROUP BY DeptNo=d_no;
RETURN d_cnt;
END get_dno;
and use this query below to get value from user.
DECLARE
get_dptno NUMBER;
BEGIN
get_dptno := get_dno(:d_no);
DBMS_OUTPUT.PUT_LINE('No of employees in searched DeptNo : ' ||get_dptno);
END;
But I couldn't even get the Function part to run.
The error I got was where I used GROUP BY, I think
This is the error message I got
Is there any workaround for the same logic ???

Answer 1

When you group by column there is no condition accept please remove code after column name DeptNo.
CREATE OR REPLACE FUNCTION get_dno (d_no IN Employee.DepartmentNo%TYPE)
RETURN NUMBER
IS
d_cnt NUMBER;
BEGIN
SELECT COUNT(*) INTO d_cnt
FROM employee GROUP BY DeptNo;
RETURN d_cnt;
END get_dno;

Answer 2

You are almost there, you want WHERE rather than GROUP BY and you need to work out if the column name is DepartmentNo or DeptNo and use the correct column name in the signature and in the SELECT query:
CREATE FUNCTION get_dno (
d_no IN Employee.DepartmentNo%TYPE
) RETURN NUMBER
IS
d_cnt NUMBER;
BEGIN
SELECT COUNT(*)
INTO d_cnt
FROM employee
WHERE DepartmentNo=d_no;
RETURN d_cnt;
END get_dno;
/
Then:
DECLARE
get_dptno NUMBER;
BEGIN
get_dptno := get_dno(:d_no);
DBMS_OUTPUT.PUT_LINE('No of employees in searched DeptNo : ' ||get_dptno);
END;
/
Works and, for the sample data:
CREATE TABLE employee (id, departmentno) AS
SELECT 1, 1 FROM DUAL UNION ALL
SELECT 2, 1 FROM DUAL UNION ALL
SELECT 3, 1 FROM DUAL UNION ALL
SELECT 4, 1 FROM DUAL UNION ALL
SELECT 5, 2 FROM DUAL UNION ALL
SELECT 6, 2 FROM DUAL UNION ALL
SELECT 7, 3 FROM DUAL UNION ALL
SELECT 8, 3 FROM DUAL UNION ALL
SELECT 9, 3 FROM DUAL UNION ALL
SELECT 10, 4 FROM DUAL;
If :dno is 1 then outputs:
No of employees in searched DeptNo : 4
db<>fiddle here