I have a table in SQL Server 2008 that for explanation purposes contains, ID, Employee and ManagerID.
eg:
ID Employee ManagerID
1 A NULL
2 B 2
3 C 2
I want to write a query that returns all non related ManagerID's and ID's where ManagerID is equal to the ID.
The result should look like this,
ID Employee ManagerID
1 A NULL
2 B 2
In essence no managers can be managers of managers.
At first I thought that it would be simple using a SELF Join and an EXCLUDE SQL statement however I cannot get this to work. I would prefer not to USE the EXCLUDE statement as my actual table has more columns and related data that I would like to return.
If you could help, I would be grateful.
select employee, managerid
from your_table
where managerid is null
or managerid = id
Related
I am having trouble wrapping my head around the on statement when doing a self-join. Let's say we have the following table:
employeeid
name
managerid
salary
1
Mike
3
35000
2
Rob
1
45000
3
Todd
NULL
25000
4
Ben
1
55000
5
Sam
1
65000
I want to perform a self join to return the employee name and their manager's name.
When I perform the following self join I get an incorrect result:
SELECT E.name as Employee,M.name as Manager
FROM tblEmployees E
LEFT JOIN tblEmployees M
ON E.Employeeid=M.managerid
However, when I reverse the columns on the on statement using the query below:
SELECT E.name as Employee,M.name as Manager
FROM tblEmployees E
LEFT JOIN tblEmployees M
ON E.managerid=M.Employeeid
I get the correct answer.
Why? How do I know which columns to select in an on statement?
Here's my explanation:
The table you have is structured with each row representing an employee in the company.
You are interested in determining who is each employee's manager.
You are able to find that by joining the table on itself where the lookup values are the manager ids (managerid) and the reference column are the employee ids (employeeid).
The first query is wrong because the employeeid column is being used for the lookup values and the managerid column is being used for reference.
To get the manager of each employee you need to look use the managerid column as the lookup column and the employeeid column as the reference column.
Hope that's not too confusing!
I am new in SQL and have problem picking the biggest value of a column for every manager_id and also other information in the same row.
Let me show the example - consider this table:
name
manager_id
sales
John
1
100
David
1
80
Selena
2
26
Leo
1
120
Frank
2
97
Sara
2
105
and the result I am expecting would be like this:
name
manager_id
top_sales
Leo
1
120
Sara
2
105
I tried using Max but the problem is that I must group it with manager_id and not being able to take name of the salesPerson.
select manager_id, max(sales) as top_sales
from table
group by manager_id ;
This is just an example and the actual query is very long and I am taking the information from different tables. I know that I can use the same table and join it again but the problem is as I mentioned this query is very long as I am extracting info from different tables with multiple conditions. And I don't want to make a temporary table to save it. It should be done in one single query and I actually did solve this but the query is super long due to the inner join that I used and made original table twice.
My question is that can I use Max and have the value in the name column or is there other method to solve this?
Appreciate all help
You can use row_number() with CTE to get the highest sales for each manager as below:
with MaxSales as (
select name, manager_id, sales,row_number() over (partition by manager_id order by sales desc) rownumber from table
)
select name , manager_id ,sales from MaxSales where rownumber=1
I am a little bit a newbie in SQL and am struggling with a seemingly easy task.
Let's see the data:
FirstName LastName ID DepartmentNumber ManagerID
Aliana Abramova 1111111111 4 4610226861
Boriana Borova 2222222222 4 4610226861
Cali Moldovanska 3333333333 4 4610226861
Anelia Simeonova 4009016246 1 4009016246
Maria Tacheva 4206174562 3 4206174562
This is an employee table. What I am trying to do is to extract these employees that are managers (ID = ManagerID) but only these out of them that work in a department that have more than one employees (so only these that have a count of ID grouped by DepartmentNumber >0)
I can do this tasks separately:
Select FirstName, LastName, ID
from Employee
where ID = ManagerID;
Select count(ID)
from Employee
group by DepartmentNumber;
It is hard for me though, to somehow merge this knowledge into one query and combined the data so that I know which are these IDs that belong to employees that are both managers and in their department work more than 1 person.
I have done similar tasks but when it comes to merging 1-2-3 tables grouped on different levels (and merged by different keys) I get somehow confused. Probably I need to make an interim select statement but now sure how.
You can use EXISTS:
SELECT *
FROM dbo.YourTable A
WHERE EXISTS(SELECT 1 FROM dbo.YourTable
WHERE DepartmentNumber = A.DepartmentNumber
GROUP BY DepartmentNumber
HAVING COUNT(*) > 1)
AND ID = ManagerID;
Looking around in the (now-discontinued) documentation and found this example:
Subquery in FROM clause
A subquery in a FROM clause acts similarly to a temporary table that is generated during the execution of a query and lost afterwards.
SELECT Managers.Id, Employees.Salary
FROM (
SELECT Id
FROM Employees
WHERE ManagerId IS NULL
) AS Managers
JOIN Employees ON Managers.Id = Employees.Id
(Excerpted from Subqueries - Subquery in FROM clause. The original author was Phrancis. Attribution details can be found on the contributor page. The source is licenced under CC BY-SA 3.0 and may be found in the Documentation archive. Reference topic ID: 1030 and example ID: 3327.)
My question is:
why using an extra ManagerId. An Id column is already in
Employees table,
why have the extra ManagerId to be null for a manager (ok it wants to be a joke).
My opinion:
despite the upvotes, something is wrong with this is example,
Tables with example data would be nice to see on the fly how it's working. One table with start data, one table temporary SELECT and one table the
resultset.
Edit: Thanks to all contributors for their answers!
#Alex K.: That is my point of view "it is not something one would actually use". But people, who wants to learn SQL, might think, that it is good practice, because it is in the documentation here.,
#Nebi: Thanks for the point that one would write it simpler to get the same result.
#Unnikrishnan R: "showcase how the sub query works" does in my eyes not only mean that it is fully functional but additional that it makes sense. If I get things simpler, why doing it the errorprone hard way.
#me: should have titled it "let's discuss sql documentation" or like that ;)
Let us consider a situation where Employee table holds all employees including their managers in which employee has an Id, and there is also a column for the manager Id (which can be null). This can be the point of view ,who was writing that SQL queries.
For Example,
+----+-------+--------+-----------+
| Id | Name | Salary | ManagerId |
+----+-------+--------+-----------+
| 1 | Joe | 70000 | 3 |
| 2 | Henry | 80000 | 4 |
| 3 | Sam | 60000 | NULL |
| 4 | Max | 90000 | NULL |
+----+-------+--------+-----------+
why have the extra ManagerId to be null for a manager --
getting the employees that are not managers
It is just an example how to do/ use Subqueries.
To your questions:
why using an extra ManagerId. An Id column is already in Employees
table
First of all ManagerId and Id are different columns of the table Employees. So there is a difference between them. But you might reffering to the Id of the Subquery Managers and the Id of the joined table Employees.
Then you need to define which Id you are using. Else you get the Error for ambigiuos column. In this example you to specify either the Subqueries Id which is Managers.Id or the Id of the joined table Employees (Employees.Id). Which one you choose is totally regardless because you use INNER JOIN one the Id.
why have the extra ManagerId to be null for a manager (ok it wants
to be a joke).
This is because of getting all the Employees that have are not managers. You are right about saying this could be done easier or in other form. For instance:
SELECT Id, Salary
FROM Employees
WHERE ManagerId IS NULL
This probably gets the same result as in the original. But the example is not about that, it is about the structure of a subquery.
why using an extra ManagerId. An Id column is already in Employees table
Consider you are having an employee table and you also wanted to keep the manager information in the same table.so apart from the ID column you need to add another column to keep the managerid.
why have the extra ManagerId to be null for a manager (ok it wants to be a joke).
The query is just to showcase how the sub query works. In this case subquery retrieves the manager from the Employee table (managerID is null) then join those id's with Employee table in the outer query to get the salary of each managers.
I'm supposed to answer this for class, and it's tricky (for me)
Write a SELECT query to output the name of all employees with the name of their supervisor. If the employee has no supervisor, the supervisor name column should contain the text 'No Supervisor'.
The primary key field in my db is the employeeid and they are provided with names, and each student also has a supervisorid
The table for this is shown below (sorry for the layout):
employeeid lastname firstname salary supervisorid
1 Stolz Ted 25000 NULL
2 Boswell Nancy 23000 1
3 Hargett Vincent 22000 1
4 Weekley Kevin 22000 3
5 Metts Geraldine 22000 2
6 McBride Jeffrey 21000 2
7 Xiong Jay 20000 3
I was wondering how I could go about this statement without using the case statement to apply each of the 7 students with:
when concat(firstname,' ',lastname)='Nancy Boswell' then 'Ted Stolz'
In larger tables this would simply be a HUGE statement, is there a better way to do it?
Thanks!
EDIT:
I've now tried this:
SELECT
EMP1.employeeid as 'employee',
EMP2.supervisorid as 'manager'
FROM
employee EMP1
LEFT OUTER JOIN
employee EMP2
ON
emp1.employeeid = emp2.supervisorid;
However, I am seeing duplicate fields, for some reason employee 2 and 3 are appearing twice, meaning there are 9 fields showing instead of 7.
Also, I need to display their names, not their id's does that mean I need to join the join that i've already done to the employee name ? How would I do this?
Thanks for the feedback guys!
You need to link the table with itself based on the supervisorId. This might be strange if you are new to SQL but it is very common to do. You tell with SQL to add the row of the supervisor to the row of the employee via its primary key.
SELECT
*
FROM
EMPLOYEES EMP1
LEFT OUTER JOIN
EMPLOYEES EMP2
ON
-- make link between tables here
Note that the above query is not 100% correct / complete, its an indication. The LEFT OUTER JOIN statement makes the employees without supervisor have null values for the supervisor, otherwise the whole record would be left out.