The following script should return the name of the departments and the number of employees that are in those departments, the Marketing,Executive and Sales departments have '0' employees but instead of '0' , the returned value is '1'. How can I correct it?
select Department, Departments.DepartmentID, count(*) as 'NumOfEmps'
from Departments
left join Employees
on Employees.DepartmentID = Departments.DepartmentID
group by Departments.DepartmentID,Department
You can't do that all in one query. You need a sub-query to get the employee counts first, then get the related department information (name, etc.) using the aggregated results:
SELECT Department, Departments.DepartmentID, t.NumOfEmps
FROM Departments
LEFT JOIN (SELECT DepartmentID, count(*) as 'NumOfEmps'
FROM Employees
GROUP BY DepartmentID) t
ON t.DepartmentID = Departments.DepartmentID
I'm making some assumptions about your schema since it's not listed. Column names may be off a bit, but this is the general idea. Hope it helps.
Don't use Count(*) count the thing you want to count namely the employees.
Count(*) counts the whole row. Since there's always going to be at least one record for each Department in Departments when you do count(*) you'll always get at least 1
SELECT d.Department, d.DepartmentID, count(e.EmployeeID)
FROM Departments d
LEFT JOIN employees e
ON d.DepartmentID = e.DepartmentID
GROUP BY
d.Department, d.DepartmentID
DEMO
Related
this is the schema Write a query to display the name of the department that has the maximum student count.
this is what is tried.
select d.department_name,count(s.student_id)
from department d left join student s
on d.department_id=s.department_id
group by d.department_name,d.department_id
order by d.department_name;
and i think there is something missing in my code
You're almost there.
Order the result in descending order on the number of students and then take the first row:
SELECT department_name
FROM
(
SELECT d.department_name,
COUNT(*) AS nr_students
FROM department d
JOIN student s
ON d.department_id = s.department_id
GROUP BY d.department_name
ORDER BY nr_students DESC
)
WHERE ROWNUM <= 1;
Based on the schema mentioned, you would have to make a join (INNER JOIN) to the department table from the staff table to get the name of the department.
If the name of the department is not desired and the counts can just be based on the department_id, then a join is not required.
The queries for both the scenarios is mentioned below.
Oracle SQL query for result with the department name, i.e. with INNER JOIN
SELECT D.DEPARTMENT_NAME, COUNT(S.DEPARTMENT_ID) AS STAFF_COUNT FROM **DEPARTMENT D, STAFF S** --INDICATES INNER JOIN IN ORACLE SQL
WHERE D.DEPARTMENT_ID = S.DEPARTMENT_ID
GROUP BY D.DEPARTMENT_NAME
ORDER BY STAFF_COUNT DESC
Oracle SQL query for result without the department name, just the department_id
SELECT S.DEPARTMENT_ID,COUNT(S.DEPARTMENT_ID) AS STAFF_COUNT FROM STAFF S
GROUP BY S.DEPARTMENT_ID
ORDER BY STAFF_COUNT DESC
Hope this helps. Cheers.
I tried this and it worked.
select department_name
from department d inner join student s
on s.department_id=d.department_id
having count(*) in (
select max(count(student_id))
from student s join department d
on d.department_id=s.department_id
group by d.department_id)
group by d.department_id,department_name;
Select * from (
SELECT D.DEPARTMENT_NAME, COUNT(S.DEPARTMENT_ID) AS STAFF_COUNT
FROM DEPARTMENT D, STAFF S
WHERE D.DEPARTMENT_ID = S.DEPARTMENT_ID
GROUP BY D.DEPARTMENT_NAME
ORDER BY STAFF_COUNT DESC)
where rownum=1;
This query will give department name that has maximum number of student count
I wondering is what I am doing right.
select distinct
Departments.Department_No, Departments.Department_Name
from
Departments
join
Employees on Departments.Department_No = Employees.Department_No
join
Jobs on Jobs.Job_ID = Employees.Job_ID
where
Departments.Department_No not in (select distinct Department_No
from Employees
where Employees.Job_ID like '%SA_REP%');
You want to display distinct values of Department Number and Department Name
You join Employees table with Department on Department Number
You join Jobs table with Employees on Job ID
You filter the result by excluding those Department Numbers of the entire Employee table that have a Job ID matching the pattern %SA_REP%
In my opinion you don't need
the join with the Jobs table
the join with the Employees table
you could maybe see if one of the other users' suggestions can bring performance improvement
SELECT DISTINCT departments.department_no,
departments.department_name
FROM departments
WHERE departments.department_no NOT IN (SELECT DISTINCT department_no
FROM employees
WHERE employees.job_id LIKE '%SA_REP%'
);
You could simply do this using NOT EXISTS instead of using a NOT IN subquery:
SELECT DISTINCT
d.Department_No
,d.Department_Name
FROM Departments d
JOIN Employees e ON d.Department_No = e.Department_No
WHERE NOT EXISTS
(select 1
from Employees e1
where e1.Job_ID like '%SA_REP%'
AND e1.Department_No = e.Department_No);
You can translate where condition without "in".
And you don't need to fetch date from "Jobs" - you don't use it
Select distinct Departments.Department_No, Departments.Department_Name
from Departments
Join Employees on Departments.Department_No = Employees.Department_No
where Employees.Job_ID not like '%SA_REP%';
I have an EmployeeDepartmetn juction table like this. I have all the departments in Depeartment table and employees in Employee table..
I want to get departments for an particular employee along with the all the departments available in depeartment table.
It should be like Select DepartmentId, DepartmentName, EmployeeID from Query.
Main criteria here is, Need to display NULL if the employee dont have that department. I am confused here...please help.
Please give Linq Query
Thanks in Advance
Put criteria in your left join:
Select distinct a.DeptID, b.DepartmentName, b.EmployeeID
From Department a
left join EmployeeDepartment b
on a.DeptID = b.DeptID and b.EmployeeID = 1 --insert employee ID here
It will show all departments (even those with no employees), then show the employee ID you chose in the third column only if that employee is assigned there.
You can do this with conditional aggregation:
select DeptId,
max(case when EmployeeId = 1 then EmployeeId end) as EmployeeId
from EmployeeDepartment ed
group by DeptId;
EDIT:
If you have a departments table as well:
select d.deptid, d.name, ed.employeeid
from Departments d left join
EmployeeDepartment ed
on d.deptid = ed.deptid and
ed.employeeid = 1;
Suppose we use PostgreSQL and have 2 tables, department and employee, the latter belonging and having a FK into the former.
We now want to do an aggregate select, where we want to put all the information from department and then some aggregate values from employee:
SELECT d.id, d.name, d.budget, count(*), avg(e.salary), max(e.age), sum(e.children)
FROM department d LEFT JOIN employee e ON e.dept = d.id
GROUP BY d.id, d.name, d.budget
I don't like that I need to specify all the columns from department in the GROUP BY - is there a way to "group by the whole table"?
And a bit more philosophical question, suppose I do GROUP BY d.id. Assuming d.id is the primary key of department, why do I need to group by all the other columns as well?
If employee is pre aggregated then there is no need to list the select columns
select *
from
department d
left join (
select
dept as id,
count(*) as count_employee,
avg(salary) as avg_salary,
max(age) as max_age,
sum(children) as sum_children
from employee
group by dept
) e using (id)
The using clause avoids the joined on column duplicity.
How do I add a subquery as a column in my SQL script?
e.g.
Select emp_no, name,gender ,
(select department_name from departments where employees.emp_no = departments.emp_no)
from employees
PS: I'm using oracle 8
Going by the semantics, what I understand is that you want an employee's department name to be shown alongside his/her other information. I would suggest you do a join instead:
Select emp_no, name, gender, department_name
from employees emp, departments dept
where emp.emp_no = dept.emp_no;
That looks reasonably sound, I would suggest some (possible typos) cleaning up: add a comma after "gender" and declare the table names, also set the subquery alias
Select employees.emp_no, employees.name, employees.gender,
(select departments.department_name from departments where employees.emp_no = departments.emp_no) as dept_name
from employees
Alternatively, a nice join would would work too, if the other data is feasible:
Select employees.emp_no, employees.name, employees.gender, departments.department_name
from employees
inner join departments on employees.emp_no = departments.emp_no
left join is the best-practice, and should be faster in performance:
Select e.emp_no, e.name, e.gender , d.department_name
from employees e left join departments d on e.emp_no = d.emp_no;
You seem to be missing comma after gender.
Select emp_no, name,gender ,
(select department_name from departments where employees.emp_no = departments.emp_no) as dept_name from employees
The below is what you need. Just added a comma after gender. This subquery would need to return only one row for each result as well or else an error will be seen.
Select emp_no, name,gender,
(select department_name from departments where employees.emp_no = departments.emp_no)
from employees
This query is your answer but it will work only if there is one column mentioned in that if we use more than one column than it will retrun an error .
"Select employee_id,first_name,
(select department_name,manager_id from departments where employees.department_id = departments.department_id) as new_column
from employees;"
can you try this:
SELECT em.emp_no, em."name",em.gender ,
(SELECTdistinctdp.department_name
FROM departments dp
WHERE em.emp_no = dp.emp_no) my_sub
FROM employees em