Oracle show all employees with greater than average salary of their department - sql

Question

I am writing a query to find employees who earn greater than the average salary within their department. I need to display the employee ID, salary, department id, and average salary of that department.
I have a query that just almost works but it keeps giving me "ORA-00904: "AVG_SAL": invalid identifier" errors. Am I doing this correctly. Why am i getting this invalid identifier error?
SELECT employee_id, salary, department_id,
(SELECT ROUND(AVG(salary),2)
FROM employees e_inner
WHERE e_inner.department_id = e.department_id) AS avg_sal
FROM employees e
WHERE salary > avg_sal
ORDER BY avg_sal DESC

Answer 1

More efficient to use analytics:
select employee_id, salary, department_id, avg_sal
from
(
SELECT employee_id, salary, department_id,
round(avg(salary) over (partition by department_id), 2) avg_sal
from emp
)
where salary > avg_sal
order by avg_sal desc

Answer 2

I don't believe you can refer to a column alias (avg_sal in this case) in a WHERE clause.
You'll need to repeat that inner query, i.e.:
SELECT employee_id, salary, department_id,
(SELECT ROUND(AVG(salary),2)
FROM employees e_inner
WHERE e_inner.department_id = e.department_id) AS avg_sal
FROM employees e
WHERE salary >
(SELECT ROUND(AVG(salary),2)
FROM employees e_inner
WHERE e_inner.department_id = e.department_id)
ORDER BY avg_sal DESC
Not great, with those two inner queries, but that's the most-straightforward way to correct the error.
Update: Haven't tested this, but try the following:
SELECT e.employee_id, e.salary, e.department_id, b.avg_sal
FROM employees e
INNER JOIN
(SELECT department_id, ROUND(AVG(salary),2) AS avg_sal
FROM employees
GROUP BY department_id) e_avg ON e.department_id = e_avg.department_id AND e.salary > e_avg.avg_sal
ORDER BY e_avg.avg_sal DESC

Answer 3

You could rewrite it as a join:
SELECT e1.employee_id
, e1.salary
, e1.department_id
, ROUND(AVG(e2.salary),2) as Avg_Sal
FROM employees e
JOIN employees e2
ON e2.department_id = e.department_id
GROUP BY
e1.employee_id
, e1.salary
, e1.department_id
HAVING e1.salary > ROUND(AVG(e2.salary),2)
Or a subquery:
SELECT *
FROM (
SELECT employee_id
, salary
, department_id
, (
SELECT ROUND(AVG(salary),2)
FROM employees e_inner
WHERE e_inner.department_id = e.department_id
) AS avg_sal
FROM employees e
) as SubqueryAlias
WHERE salary > avg_sal

Answer 4

select *
from employees e
join(
select Round(avg(salary)) AvgSal,department_id,department_name as dept_name
from employees join departments
using (department_id)
group by department_id,department_name
) dd
using(department_id)
where e.salary > dd.AvgSal;
another solution
select *
from employees e,
(
select
department_id,
avg(salary) avg_sal
from employees
group by department_id
) e1
where e.department_id=e1.department_id
and e.salary > e1.avg_sal