I am stuck at the following SQL query:
Find the name of the departments having more than 12 instructors.
Ans should be given according to the given diagram.
Should be something like this:
select dept_name
, count(ID)
from instructor
group by dept_name
having count(ID) > 12
use the group by and having clauses to filter on an aggregation function.
select d.dept_name
from department d
inner join instructor i
on i.dept_name = d.dept_name
group by d.dept_name
having count(*) > 12
Related
Following the tutorial on SQL here I want to query the number of employees per department together with the department name.
I tried the following query in that tutorial:
SELECT count(*), dept_name
FROM employees, departments
WHERE employees.dept_id = departments.dept_id
GROUP BY departments.dept_id
but it returns
COUNT(*) dept_name
2 NULL
2 NULL
instead of the expected output
COUNT(*) dept_name
2 Accounting
2 Sales
What am I doing wrong here?
First use JOIN instead of WHERE
Then you group by dept_id to make sure you dont have duplicate name like 2 Sales department or 2 employee with same name.
SELECT departments.dept_id, dept_name, count(*)
FROM employees
JOIN departments
ON employees.dept_id = departments.dept_id
GROUP BY departments.dept_id, departments.dept_name
Group by dept_name not dept_id
SELECT count(*), dept_name
FROM employees, departments
WHERE employees.dept_id = departments.dept_id
GROUP BY departments.dept_name
And you can better use join like Juan Carlos Oropeza's answer:
SELECT count(*), dept_name
FROM employees JOIN departments ONemployees.dept_id = departments.dept_id
GROUP BY departments.dept_name
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 want to get the number of employees by department and I wrote this script using Oracle but it always says that there is a missing expression
The columns used in my tables :
department :name (the name of the department) -
depnum (the id of the department"primary key"),
employee : empnum (the id of the employee) -
depnum (the id of the department in which the employee in question is working "foreign key")
Query:
select
s.name
from
department s
inner join
employee p on s.depnum = p.depnum
group by
s.name
having
count(p.empnum) = max(select count(p.empnum)
from employee p, department s
where s.depnum = p.depnum
group by s.name) ;
If you want the number of employees by department, I would expect something like this:
select s.name, count(*) as num_employees
from department s inner join
employe p
on s.depnum = p.depnum
group by s.name ;
If you want the department names with the maximum number of names, you can use a having clause:
select s.name, count(*) as num_employees
from department s inner join
employe p
on s.depnum = p.depnum
group by s.name
having count(*) = (select max(cnt)
from (select count(*) as cnt
from employee e2
group by e2.depnum
) e2
);
The problem with your query is that you are attempting to take the max() of a subquery. That syntax is not allowed -- and not necessary.
you sql statement is not correct that's why it thrown that error. I think you tried something like below
select s.name
from department s
inner join employe p on s.depnum=p.depnum
group by s.name
having count(p.empnum)=
select max(cnt) from
(
select count(p.empnum) as cnt
from employe p join department s
on s.depnum=p.depnum
group by s.name
) t;
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
My tables are structured like this (there are more values in the tables but I only wrote the ones relevant to this):
Department(dep_id, dep_name)
Employee(dep_id)
I need to display dep_name and the number of employees in every department, except once specific department (let's call it DepX) and only the departments with more than one employee.
I tried multiple methods to solve this but none of them worked.
Some methods I tried:
SELECT department.dep_name, COUNT(employee.dep_id) AS NumberOfEmployees FROM employee
INNER JOIN department ON employee.dep_id=department.dep_id
WHERE dep_name<>'DepX'
GROUP BY dep_id
HAVING COUNT(employee.dep_id) > 1;
SELECT dep_name FROM department
WHERE dep_name <>'DepX'
UNION
SELECT COUNT(*) FROM employee
WHERE COUNT(*) > 1
GROUP BY dep_id;
I can't figure this out. Thanks!
The first example does now work because you're including dep_name in your results without an aggregation but not grouping on it.
You can either use the department name in your grouping instead of the ID:
SELECT department.dep_name, COUNT(employee.dep_id) AS NumberOfEmployees FROM employee
INNER JOIN department ON employee.dep_id=department.dep_id
WHERE dep_name<>'DepX'
GROUP BY department.dep_name
HAVING COUNT(employee.dep_id) > 1;
or do the COUNT in a subquery:
SELECT department.dep_name,
e.NumberOfEmployees
FROM department
INNER JOIN (SELECT dep_id,
COUNT(*) NumberOfEmployees
FROM employee
GROUP BY dept_id
HAVING COUNT(dept_id) > 1
) e
ON department.dep_id = e.dep_id
WHERE dep_name<>'DepX'
SELECT department.dep_name, COUNT(employee.dep_id) AS NumberOfEmployees FROM employee
INNER JOIN department ON employee.dep_id=department.dep_id
WHERE department.dep_name not in('DepX')
GROUP BY department.dep_name
HAVING COUNT(employee.dep_id) > 1;
update your table alias per your need
TEST this. This query help you return not only dept_name, it can return all fields from Department if you want:
SELECT d.*, A.numOfEmployees
FROM Department d,
(
SELECT e.dep_id, COUNT(*) numOfEmployees
FROM Employee e
GROUP BY e.dep_id
HAVING COUNT(*) > 1
) A
WHERE d.dep_id = A.dep_id
AND d.dep_name != 'DepX'