SQL hierarchyid type issue - sql

Question

The full task sounds like this: Display the content of employees whose immediate supervisor is younger and less employed in the company.
Columns:
Manager Name | Date of hiring a manager | Head's date of birth
Employee name | Employee hiring date | Employee's date of birth
I already broke my head here:
SELECT
LastName + ' ' + FirstName AS SupervisorFullName,
HireDate,
BirthDate,
(SELECT LastName + ' ' + FirstName
FROM HumanResources.Employee AS subHrE
WHERE HrE.OrganizationNode.IsDescendantOf(subHrE.OrganizationNode) = 1
AND HrE.OrganizationLevel = HrE.OrganizationNode.GetLevel() + 1) AS EmployeeFullName,
(SELECT HireDate
FROM HumanResources.Employee AS subHrE
WHERE HrE.OrganizationNode.IsDescendantOf(subHrE.OrganizationNode) = 1
AND HrE.OrganizationLevel = HrE.OrganizationNode.GetLevel() + 1) AS HireDateEmp,
(SELECT BirthDate
FROM HumanResources.Employee AS subHrE
WHERE HrE.OrganizationNode.IsDescendantOf(subHrE.OrganizationNode) = 1
AND HrE.OrganizationLevel = HrE.OrganizationNode.GetLevel() + 1) AS BithDateEmp
FROM
HumanResources.Employee as HrE
JOIN
Person.Person as P ON HrE.BusinessEntityID = P.BusinessEntityID
ORDER BY
SupervisorFullName ASC
Output
AdventureWork2016 db is used for work
Full Schema AW2016

Answer 1

There's definitely a certain way to think about use of hierarchyid that, once you get the hang of it, opens a lot of possibilities. Here's what I came up with:
WITH FullPerson AS (
SELECT CONCAT_WS(' ', p.FirstName, p.MiddleName, p.LastName) AS [FullName],
e.HireDate,
e.BirthDate,
e.OrganizationNode
FROM HumanResources.Employee AS e
JOIN Person.Person AS p
ON p.BusinessEntityID = e.BusinessEntityID
)
SELECT
manager.OrganizationNode.ToString(),
manager.FullName,
manager.HireDate,
manager.BirthDate,
subordinate.OrganizationNode.ToString(),
subordinate.FullName,
subordinate.HireDate,
subordinate.BirthDate
FROM FullPerson AS subordinate
JOIN FullPerson AS manager
ON subordinate.OrganizationNode.GetAncestor(1) = manager.OrganizationNode
WHERE manager.HireDate > subordinate.HireDate
AND manager.BirthDate > subordinate.BirthDate;
Breaking it down, I create a common table expression to join Employee and Person as I'll need columns from both tables for both subordinates and their managers. The real trick is the join condition. subordinate.OrganizationNode.GetAncestor(1) = manager.OrganizationNode says "take the subordinate's OrganizationNode and go one level up the tree". What's amazing to me is that this sort of query can be supported by indexes and indeed there is an index on that column in the AdventureWorks schema! In addition to the columns you asked for, I added a human-readable representation of OrganizationNode to help with the visualization of how the data relates.