I have a table Employee which contains Employee id and Manager id. I want to get Employee id, Employee's Manager id, and Employee's manager's Manager id.
I can get it using self join and other joins like
Select employe id, Manager id
from emplyee as a, employee as b
where a.manager_id = b.employee id
But is there a better way? Can we do this without joins, by only querying the table once?
If you don't consider a co-related subquery as a join you can do this:
Select e.employee_id,
e.manager_id,
(select manager_id
from employee e2
where e2.employee_id = e.manager_id) as employee_manager_id
from employee e;
But at some point you have to do some kind of "join".
you can use recursive CTE but still you have to use a join
Look at this example:
WITH MyCTE
AS (
SELECT EmpID, FirstName, LastName, ManagerID
FROM Employee
WHERE ManagerID IS NULL
UNION ALL
SELECT EmpID, FirstName, LastName, ManagerID
FROM Employee
INNER JOIN MyCTE ON Employee.ManagerID = MyCTE.EmpID
WHERE Employee.ManagerID IS NOT NULL
)
SELECT *
FROM MyCTE
please refer to this link for detail of CTE by Pinal Dave
http://blog.sqlauthority.com/2012/04/24/sql-server-introduction-to-hierarchical-query-using-a-recursive-cte-a-primer/
Related
I wrote a query which gives me top 3 salaries for the specific department id. For example for DepartmentId=100:
select distinct top 3 e.Id, e.Salary, dep.Id
from Employee e
inner join Department dep on e.DepartmentId = dep.Id and dep.Id = 100
and it's working fine.
Now, I want to run previous query for every department id and union all results. Something like this (written in a pseudocode):
Result <- empty
foreach depId in [Department].id
Result = Result UNION run previous query with depId (insead of 100)
How can I achive this with SQL?
If you only need the department's id in the results (and not its name also) then the join is not necessary because this id exists in the table Employee.
Use row_number() window function:
select e.Id, e.Salary, e.DepartmentId
from (
select
Id, Salary, DepartmentId,
row_number() over (partition by DepartmentId order by Salary desc) rn
from Employee
) e
where e.rn <= 3
You can use APPLY
select t.Id, t.Salary, t.DepartmentId
from Department dep
cross apply (
select distinct top 3 e.Id, e.Salary, e.DepartmentId
from Employee e
where e.DepartmentId = dep.Id) t
This will only return Employee rows for which parent Department exists.
There are two tables, employee and dept:
How can I join the two tables and select the department with the least number of employees?
It would have been better to answer if you provided the table structure.
But give this a try:
SELECT deptname
FROM dept
WHERE deptid = (SELECT distinct deptid
FROM employee
ORDER BY COUNT(dept) limit 1);
Please try the following...
SELECT deptid,
deptname,
employeeCount
FROM
(
SELECT dept.deptid AS deptid,
dept.deptname,
COUNT( dept.deptid ) AS employeeCount
FROM dept
JOIN employee ON dept.deptid = employee.deptid
GROUP BY dept.deptid,
dept.deptname
)
GROUP BY deptid
HAVING employeeCount = MIN( employeeCount );
This statement starts with the inner query joining dept to employee on the shared field deptid. It then groups the resulting rows by department and returns to the outer query the department's id and name along with a count of employees for that department.
The outer query groups the data by department again, then selects the details of the department(s) having a count of employees equal to the minimum count of employees.
If you have any questions or comments, then please feel free to post a Comment accordingly.
I'm only answering because MIN isn't needed and LIMIT isn't Oracle:
select d.*
from (select deptid, count(*) as cnt
from employees e
group by deptid
order by count(*) asc
) d
where rownum = 1;
In Oracle 12C+, you don't need the subquery:
select deptid, count(*) as cnt
from employees e
group by deptid
order by count(*) asc
fetch first 1 row only;
Hi :) so my answer is a bit ugly, and full of nested queries. but I tested it and it worked for me...
-- First I created a couple of test tables and added a few records
drop table dept;
drop table employee;
create table dept (deptid number primary key, deptname varchar(20));
create table employee(employee_id number primary key, names varchar(20),
deptid number,foreign key (deptid) references dept(deptid));
insert into dept values(1,'HR');
insert into dept values(2,'Finance');
insert into dept values(3,'IT');
insert into employee values(1,'Tina',1);
insert into employee values(2,'Rob',1);
insert into employee values(3,'Lisa',1);
insert into employee values(4,'Will',2);
insert into employee values(5,'Lina',2);
insert into employee values(6,'Ethel',2);
insert into employee values(7,'Trevor',1);
insert into employee values(8,'Alanea',1);
insert into employee values(9,'Matthew',1);
insert into employee values(10,'Maddie',3);
insert into employee values(11,'Anna',1);
-- According to the added records, the answer we are looking for should be
the department name IT
-- select the department name from department table
select d.deptname from dept d,
/* This is where it gets ugly - basically, it counts the number of
employees in each department, then finds the id of the department that had
the smallest count */
(select deptid from
(select count(deptid) as counter, deptid from employee group by deptid)
where counter =( select min(counter)from
(select count(deptid) as counter, deptid from employee group by deptid))) minid
-- join the tables using deptid
where d.deptid = minid.deptid;
This query gave the correct answer for me even when I changed the records to make finance the correct answer.
If you have any questions give me a yell through the comments :)
select department_name, count(employee_id)
from department d
inner join employee e
on d.employee_id = e.employee_id
having count(employee_id) =
(
select min(count(employee_id)) /*This query returns minimum count*/
from department d
inner join employee e
on d.employee_id = e.employee_id
group by department_name
)
group by department_name;
WITH temp
AS
(SELECT e1.department_id, count(e1.employee_id) emp_count
FROM hr.employees e1
GROUP BY e1.department_id)
SELECT d1.department_name, t1.emp_count employee_count
FROM temp t1
,hr.departments d1
WHERE t1.department_id = d1.department_id(+)
AND NOT EXISTS
(SELECT 1
FROM temp t2
WHERE t2.emp_count < t1.emp_count)
ORDER BY 2,1 ;
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;
There are two tables as below
employee table: empid, empname, deptid
department table: deptid, deptname
then write query to "list all employees for dept name=computer"
this should be pretty straight forward,
SELECT a.empid, a.empname, b.deptname
FROM employee a
INNER JOIN department b
ON a.deptid = b.deptid
ORDER BY b.deptname, a.empname
SQLFiddle Demo
To further gain more knowledge about joins, kindly visit the link below:
Visual Representation of SQL Joins
SELECT empname, deptname
from employee, department
where employee.deptid=department.deptid
and department.deptname='computer';
Computer must be case sensitive as per your values in your table
SELECT e.empname, deptname
FROM employee e
INNER JOIN department d
ON e.deptid = d.deptid
GROUP BY emptname, deptname
T1: employee [id, salary]
T2: department [name, employeeid]
(employeeid is a foreign key to T1's id)
Problem: Write a query to fetch the name of the department which receives the maximum salary.
My Solution:
SELECT DISTINCT name
FROM department AS a
INNER JOIN employee AS b ON a.employeeid = b.id
AND b.salary
IN (
SELECT max( salary )
FROM employee AS c
)
Edit: The problem statement is accurate, and we're not trying to find out the employee who has the highest salary. It says "....Department which receives.....", not "...employee who receives....".
Is this ok? Or can this be optimized?
GROUP BY the name of the department and order by SUM(salary).
SELECT department.name
FROM department
JOIN employee ON department.employeeid = employee.id
GROUP BY department.name
ORDER BY SUM(salary) DESC
LIMIT 1
How about:
SELECT employee.id, employee.salary, department.name
FROM department, employee
where
employee.id = department.employeeid and
employee.salary = (select max(salary) from employee)