Need to retrieve columns from 3 tables - sql

Question

There are three tables: dept, emp, sal . You can find their structure and data in the images.
I need to extract the list of employees who have location as pune and have max salary in their department. Since there are five departments, the final output will contain five rows and columns of emp_id, dept, dept_id, salary.
I've tried...
select e.emp_id, dept,e.dept_id, max(sal) as 'highest salary'
from sal s,emp e,dept d
where e.emp_id = s.emp_id and d.dept_id = e.dept_id and loc ='Pune'
group by e.emp_id,e.dept_id,dept
order by e.dept_id

Answer 1

I would use apply :
select t.emp_id, d.dept, d.dept_id, t.sal
from dept d
cross apply ( select top 1 e.emp_id, s.sal as sal
from emp e
inner join sal s on s.emp_id = e.emp_id
where d.dept_id = e.dept_id and e.loc = 'Pune'
order by s.sal desc
) t;

Answer 2

Unless you have window functions (that depends on whether you're using MySQL, Oracle, SQLite, etc) you will need to do it in two steps.
Find the highest salary per department (for employees in 'Pune'), then another set of joins to find out who those people are.
SELECT
dep.dept,
dep.dept_id,
emp.emp_id,
sal.sal
FROM
emp
INNER JOIN
sal
ON sal.emp_id = emp.emp_id
INNER JOIN
(
SELECT
emp.dept_id,
MAX(sal.sal) AS max_sal
FROM
emp
INNER JOIN
sal
ON sal.emp_id = emp.emp_id
WHERE
emp.loc = 'Pune'
)
dep_sal
ON dep_sal.dept_id = emp.dept_id
AND dep_sal.max_sal = sal.sal
INNER JOIN
dep
ON dep.dept_id = emp.dept_id
WHERE
emp.loc = 'Pune'
ORDER BY
dep.dept,
emp.emp_id
EDIT: With SQL Server 2008 on-wards it's a bit easier...
WITH
emp_sal_ranked AS
(
SELECT
emp.dept_id,
emp.emp_id,
sal.sal,
RANK(sal.sal) OVER (PARTITION BY emp.dept_id
ORDER BY sal.sal
)
AS rank_sal
FROM
emp
INNER JOIN
sal
ON sal.emp_id = emp.emp_id
WHERE
emp.loc = 'Pune'
)
SELECT
dep.dept,
dep.dept_id,
emp_sal_ranked.emp_id,
emp_sal_ranked.sal
FROM
emp_sal_ranked
INNER JOIN
dept
ON dept.dept_id = emp_sal_ranked.dept_id
WHERE
emp_sal_ranked.rank_sal = 1
ORDER BY
dep.dept,
emp_sal_ranked.emp_id