GROUP BY - inline view and unjoined tables - sql

Question

I have the following ORACLE query where I attempt to find the department with the highest average salary. I would like to use in-line view (i.e. retain the b dataset) for this implementation, but struggle to get the right part at the WHERE and GROUP BY components. I know the below GROUP BY and WHERE (which is non-existant) is wrong. But how do i correct them?
select a.deptno from emp a,
(select max(avg_sal) max_avg_sal from (select
avg(sal) avg_sal from emp group by deptno) ) b
group by a.deptno, b.max_avg_sal
having avg(a.sal) = b.max_avg_sal
Expected Result
deptno
10
Emp Structure
deptno staff sal
10 A 1000
10 B 1500
11 C 1100
12 D 1000
12 E 900
12 F 1000

Answer 1

Is this what you want?
select e.*
from (select e.*, avg(e.salary) over (partition by e.deptno) as avg_salary
from emp e
) e
order by avg_salary desc
fetch first 1 row only;
fetch first is available in Oracle 12c+. You can do similar things with an additional subquery in earlier versions.

Answer 2

You can use subquery
select deptno from tablename
group by deptno
having avg(sal)= (select max(asal) from (select avg(sal) as asal from tablename group by deptdno)A)

Answer 3

The straight-forward way is:
select deptno
from emp
group by deptno
order by avg(salary) desc
fetch first row with ties;
FETCH FIRST is available as of Oracle 12c.
In Oracle 11g we could use this instead:
select deptno
from
(
select deptno, avg(salary) as avg_salary, max(avg(salary)) over () as max_avg_salary
from emp
group by deptno
)
where avg_salary = max_avg_salary;
But you want an inline view, another word for a derived table (a subquery in the from clause). That looks way more clumsy. One example without FETCH FIRST and without window functions:
with d as
(
select deptno, avg(salary) as avg_salary
from emp
group by deptno
)
, dmax as
(
select max(avg_salary) as max_avg_salary
from d
)
select d.*
from d
join dmax on dmax.max_avg_salary = d.avg_salary;
I find this very obfuscated and don't recommend it at all. You can do the same without WITH clauses of course. Then it is even less readable.

Answer 4

I don't know why you'd want to write it this way, but if you really want only inline views and no windowing clauses, you can write it this way:
select b.deptno
from (SELECT deptno, avg(sal) avgsal from emp group by deptno ) b
cross join (SELECT max(avgsal) maxavgsal FROM (SELECT avg(sal) avgsal FROM emp group by deptno )) c
where b.avgsal = c.maxavgsal;
This the same thing, if you don't like CROSS JOIN for some reason:
select b.deptno
from (SELECT deptno, avg(sal) avgsal from emp group by deptno ) b
inner join ( SELECT max(avgsal) maxavgsal FROM
( SELECT avg(sal) avgsal FROM emp group by deptno ) ) c
on b.avgsal = c.maxavgsal;