Error: ORA-00937 - plsql

Question

I want to create a table NEW_DEPTS. I have DEPARTMENT_ID and DEPARTMENT_NAME which is in DEPARTMENTS table.
desc departments
Name Null? Type
------------------------------- -------- ----
DEPARTMENT_ID NOT NULL NUMBER(4)
DEPARTMENT_NAME NOT NULL VARCHAR2(30)
MANAGER_ID NUMBER(6)
LOCATION_ID NUMBER(4)
My EMPLOYEES table contains:
desc employees
Name Null? Type
------------------------------- -------- ----
EMPLOYEE_ID NOT NULL NUMBER(6)
FIRST_NAME VARCHAR2(20)
LAST_NAME NOT NULL VARCHAR2(25)
EMAIL NOT NULL VARCHAR2(25)
PHONE_NUMBER VARCHAR2(20)
HIRE_DATE NOT NULL DATE
JOB_ID NOT NULL VARCHAR2(10)
SALARY NUMBER(8,2)
COMMISSION_PCT NUMBER(2,2)
MANAGER_ID NUMBER(6)
DEPARTMENT_ID NUMBER(4)
Now, I want to create a table NEW_DEPTS which should contain DEPARTMENT_ID and DEPARTMENT_NAME along with total SALARY that each Department has. Every department have certain number of employees, so, for department number 10, 20, 30, and so on, total Salary should be calculated.
My main query is:
create table new_depts as
select d.department_id,d.department_name,sum(e.salary) dept_sal
from employees e,departments d
where e.department_id = d.department_id;
I got an Error:
select d.department_id,d.department_name,sum(e.salary) dept_sal
*
ERROR at line 2:
ORA-00937: not a single-group group function
So, I googled it. I found that group function like sum, avg, max, min can't be used in select statement. I needed GROUP BY clause. So, I wanted to solve it individually. Therefore, I skipped the "create table..." statement and wrote:
select distinct d.department_id,d.department_name,sum(e.salary) dept_sal
from employees e,departments d
where e.department_id = d.department_id
group by department_id;
I got Error:
group by department_id;
*
ERROR at line 4:
ORA-00911: invalid character
Then I wrote:
select d.department_id,d.department_name,sum(e.salary) dept_sal
from employees e,departments d
where e.department_id = d.department_id
group by d.department_id;
I got Error:
select d.department_id,d.department_name,sum(e.salary) dept_sal
*
ERROR at line 1:
ORA-00979: not a GROUP BY expression
Then I wrote:
select d.department_id,d.department_name,sum(e.salary) dept_sal
from employees e,departments d
where e.department_id = d.department_id
group by department_id;
I got Error:
group by department_id
*
ERROR at line 4:
ORA-00918: column ambiguously defined
I know that its a "join". But not getting how should I place GROUP BY clause so that my GROUP FUNCTION may run correctly.

Answer 1

You need to group by all columns not in an aggregate function and since you have defined a table alias you must use that in your columns. The error ORA-00918: column ambiguously defined is because you have two columns named department_id so you must specify the table the department_id is from:
select d.department_id,
d.department_name,
sum(e.salary) dept_sal
from employees e
inner join departments d
on e.department_id = d.department_id
group by d.department_id, d.department_name;
You will notice that I altered the query to use ANSI JOIN syntax (INNER JOIN).