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

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

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 2

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 3

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