I have the following table:
I have to find the name and the country of the department with the highest number of employees.
SELECT d.department_name, c.country_name FROM employees e, departments d, locations l, countries c
WHERE d.location_id = l.location_id AND l.country_id = c.country_id
HAVING MAX(e.employee_id) = (SELECT MAX(MAX(employee_id)) FROM employees GROUP BY department_id);
I'm getting a not a single-group group function error. Why is that?
If am not wrong this is what you are looking for
SELECT *
FROM (SELECT d.department_name,
c.country_name
FROM employees e
INNER JOIN departments d
ON e.department_id = d.department_id
INNER JOIN locations l
ON d.location_id = l.location_id
INNER JOIN countries c
ON l.country_id = c.country_id
GROUP BY d.department_name,
c.country_name
ORDER BY Count(1) DESC)
WHERE ROWNUM = 1
is this what you want?
SELECT d.department_name, c.country_name FROM employees e, departments d, locations l, countries c
WHERE d.location_id = l.location_id AND l.country_id = c.country_id
AND ROWNUM = 1
ORDER BY e.employee_id DESC
Related
I am using this code:
create or replace view VIEW_MAXMIN as
select c.country_name,
max(salary) max_salary,
min(salary) min_salary
from employees e,
departments d,
locations l,
countries c
where e.department_id = d.department_id
and d.location_id = l.location_id
and l.country_id = c.country_id = not in(select country_name
from countries
where country_name = 'Mexico');
but always error saying 'SQL command not properly ended'
You can change the joins from legacy Oracle comma joins to ANSI joins and then it looks like you want countries where the name is not Mexico.
Also, if you are aggregating columns and have a column that you are not aggregating then you need to use GROUP BY:
create or replace view VIEW_MAXMIN as
select c.country_name,
max(salary) max_salary,
min(salary) min_salary
from employees e
INNER JOIN departments d
ON (e.department_id = d.department_id)
INNER JOIN locations l
ON (d.location_id = l.location_id)
INNER JOIN countries c
ON (l.country_id = c.country_id)
where c.country_name != 'Mexico'
GROUP BY c.country_name;
Looks like the error you're getting in particular is due to -
l.country_id = c.country_id = not in(select country_name
from countries
where country_name = 'Mexico');
You have 2 equals to condition in one filter statement - like a = b = c
Just - l.country_id = c.country_id would suffice and country_name != 'Mexico' will have to be a separate condition
I need to find the a list of people who earn more money than the average salary in their country
SELECT e1.first_name || ' ' ||e1.last_name
FROM hr.employees e1
WHERE salary >= (
Select AVG(salary)
FROM HR.employees e2
INNER JOIN HR.departments ON e2.department_id = departments.department_id
INNER JOIN HR.locations ON HR.departments.location_id = HR.locations.location_id
INNER JOIN HR.countries ON HR.locations.country_id = hr.countries.country_id
GROUP BY hr.countries.country_id
);
The subquery gives me the average salary values per country and works right.
However when I try to combine them I get the following error:
ORA-01427: Subquery returns more than one row
Any idea what I should do to get the query working?
Use AVG as an analytic function:
SELECT full_name
FROM (
SELECT e.first_name || ' ' ||e.last_name AS full_name,
e.salary,
AVG( e.salary ) OVER ( PARTITION BY l.country_id ) AS avg_salary
FROM hr.employees e
INNER JOIN HR.departments d
ON e.department_id = d.department_id
INNER JOIN HR.locations l
ON d.location_id = l.location_id
)
WHERE salary > avg_salary;
Use window functions:
SELECT e.first_name || ' ' || e.last_name
FROM (SELECT e.*,
AVG(salary) OVER (PARTITION BY l.country_id) as country_avg
FROM HR.employees e JOIN
HR.departments d
ON e.department_id = d.department_id JOIN
HR.locations l
ON d.location_id = l.location_id
) e
WHERE e.salary >= e.country_avg;
Note that the country table is not needed. The country_id is sufficient to identify the country.
How can I write a query that gives the country name, city, postal code, street address and the number of departments where at least 2 employees work? Below is the query I wrote, but I get "not a GROUP BY expression" error as a result of the query.
SELECT k.COUNTRY_NAME,
l.CITY,
l.POSTAL_CODE,
l.STREET_ADDRESS,
e.DEPARTMENT_ID,
COUNT(EMPLOYEE_ID)
FROM hr.employees e
JOIN hr.departments c
ON (c.DEPARTMENT_ID = e.DEPARTMENT_ID)
JOIN hr.locations l
ON (c.LOCATION_ID = l.LOCATION_ID)
JOIN hr.countries k
ON (k.COUNTRY_ID = l.COUNTRY_ID)
GROUP BY e.DEPARTMENT_ID
HAVING COUNT(EMPLOYEE_ID) > 2;
Because all non-aggregated columns(c.country_name,l.city,l.postal_code,l.street_address,e.department_id) should be listed within the GROUP BY list which is not suitable for your case. Rather use COUNT(.) OVER (..) analytic function with PARTITION BY e.department_id option in order to group by department_id column such as
SELECT DISTINCT *
FROM
(
SELECT c.country_name,
l.city,
l.postal_code,
l.street_address,
e.department_id,
COUNT(e.employee_id) OVER (PARTITION BY e.department_id) AS count
FROM hr.employees e
JOIN hr.departments d
ON d.department_id = e.department_id
JOIN hr.locations l
ON d.location_id = l.location_id
JOIN hr.countries c
ON c.country_id = l.country_id
)
WHERE count >= 2 -- equality is added considering "at least" 2
ORDER BY count
Btw, the parentheses next to the ON clause are redundant
You would first get the set of all departments that have at least 2 employees as follows(atleast_two)
After that you would join the data with the rest of your query and pull the attributes of interest.
with atleast_two
as (select c.DEPARTMENT_ID
,count(employee_id) as cnt_employees
from hr.employees e
join hr.departments c
on (c.DEPARTMENT_ID=e.DEPARTMENT_ID)
group by c.deptid
having count(employee_id)>2
)
select k.COUNTRY_NAME
, l.CITY
, l.POSTAL_CODE
, l.STREET_ADDRESS
, e.DEPARTMENT_ID
, c.cnt_employees
from hr.employees e
join atleast_two c
on (c.DEPARTMENT_ID=e.DEPARTMENT_ID)
join hr.locations l
on (c.LOCATION_ID=l.LOCATION_ID)
join hr.countries k
on (k.COUNTRY_ID=l.COUNTRY_ID);
Is it possible to retrieve the number of departments and the number of employees working in that department if given the location Id? Location_id column is in the departments table. Employees and Department share department_id column
Cannot get the correct result with this query:
select
count(E.employee_id), count(D.DEPARTMENT_ID)
from
employees e
join
departments d on (e.department_id = d.department_id)
where
D.LOCATION_ID = 1700;
I suspect you need distinct when counting the departments:
SELECT
COUNT( E.employee_id )
, COUNT(DISTINCT d.department_id )
FROM employees e
JOIN departments d ON e.department_id = d.department_id
WHERE d.location_id = 1700;
or, you need to group by department:
SELECT
COUNT( E.employee_id )
, d.department_id
FROM employees e
JOIN departments d ON e.department_id = d.department_id
WHERE d.location_id = 1700
GROUP BY d.department_id;
I am currently learing SQL and I can't understand why these two queries return different numbers of rows (the first one returns 53, while the second returns 69).
SELECT d.department_name "dept_name",
j.job_title "job_title",
e.manager_id "manager_id",
MAX(e.salary) "max_salary",
SUM(e.salary) "sum_salary"
FROM employees e, jobs j, departments d
WHERE j.job_id = e.job_id AND
d.department_id(+) = e.department_id
GROUP BY GROUPING SETS( (d.department_name, j.job_title), (j.job_title,e.manager_id), ());
And the second one:
SELECT d.department_name AS "dept_name",
j.job_title AS "job_title",
e.manager_id AS "manager_id",
MAX(e.salary) AS "max_salary",
SUM(e.salary) AS "sum_salary"
FROM employees e
INNER JOIN jobs j ON j.job_id = e.job_id
RIGHT OUTER JOIN departments d ON d.department_id = e.department_id
GROUP BY GROUPING SETS( (d.department_name, j.job_title), (j.job_title,e.manager_id), ());
Thank you for your help!
Your queries differ because in the first one you outer join table departments, whereas in the second you outer join jobs and employees. (Which is why I don't like right outer joins so much. I don't find them very readable.) You take employees, join with jobs and then by RIGHT OUTER JOIN you say: and give me all departments anyhow, so give me additional (outer joined records) for jobs and employees. The second statement is equal to:
SELECT d.department_name AS "dept_name",
j.job_title AS "job_title",
e.manager_id AS "manager_id",
MAX(e.salary) AS "max_salary",
SUM(e.salary) AS "sum_salary"
FROM departments d
LEFT OUTER JOIN employees e ON e.department_id = d.department_id
LEFT OUTER JOIN jobs j ON j.job_id = e.job_id
GROUP BY GROUPING SETS( (d.department_name, j.job_title), (j.job_title,e.manager_id), ());
In old Oracle syntax you would write:
SELECT d.department_name "dept_name",
j.job_title "job_title",
e.manager_id "manager_id",
MAX(e.salary) "max_salary",
SUM(e.salary) "sum_salary"
FROM employees e, jobs j, departments d
WHERE e.department_id(+) = d.department_id
AND j.job_id(+) = e.job_id;
In old-style joins the syntax
FROM employees e, departments d
WHERE d.department_id(+) = e.department_id
is a left join and is equal to:
FROM employees e
LEFT JOIN departments d ON d.department_id = e.department_id
For these queries two work exactly the same, you should also change the RIGHT JOIN to LEFT JOIN in the second query, or d.department_id(+) = e.department_id to d.department_id = e.department_id(+) in the first.