Recursive Queries in SQL Server 2005

Ricardo Costa — Thu, 24 May 2007 09:53:00 +0000

For building recursive queries In SQL Server 2005 we have to use a new functionality called Common Table Expressions.

Let's see how we can retrieve all the employees that report to a manager (ManagerID = 3) in the AdventureWorks database sample:

WITH CTE (EmployeeID, FullName, Title, ManagerID) AS
(

SELECT E.EmployeeID, C.FirstName + ' ' + C.LastName FullName, E.Title, E.ManagerID
FROM HumanResources.Employee E
INNER JOIN Person.Contact C ON E.ContactID = C.ContactID
INNER JOIN CTE ON E.ManagerID = CTE.EmployeeID
)

SELECT * FROM CTE

This query returns the following results:

EmployeeID	Full Name	Title	ManagerID
3	Roberto Tamburello	Engineering Manager	12
4	Rob Walters	Senior Tool Designer	3
9	Gail Erickson	Design Engineer	3
11	Jossef Goldberg	Design Engineer	3
158	Dylan Miller	Research and Development Manager	3
263	Ovidiu Cracium	Senior Tool Designer	3
267	Michael Sullivan	Senior Design Engineer	3
270	Sharon Salavaria	Design Engineer	3
5	Thierry D'Hers	Tool Designer	263
265	Janice Galvin	Tool Designer	263
79	Diane Margheim	Research and Development Engineer	158
114	Gigi Matthew	Research and Development Engineer	158
217	Michael Raheem	Research and Development Manager	158

If we don't want to return the manager we change the WHERE clause:

WITH CTE (EmployeeID, FullName, Title, ManagerID) AS
(

SELECT * FROM CTE

And the results are:

EmployeeID	Full Name	Title	ManagerID
4	Rob Walters	Senior Tool Designer	3
9	Gail Erickson	Design Engineer	3
11	Jossef Goldberg	Design Engineer	3
158	Dylan Miller	Research and Development Manager	3
263	Ovidiu Cracium	Senior Tool Designer	3
267	Michael Sullivan	Senior Design Engineer	3
270	Sharon Salavaria	Design Engineer	3
5	Thierry D'Hers	Tool Designer	263
265	Janice Galvin	Tool Designer	263
79	Diane Margheim	Research and Development Engineer	158
114	Gigi Matthew	Research and Development Engineer	158
217	Michael Raheem	Research and Development Manager	158

If we want to get all the employees that an employee reports to, we just have to change the INNER JOIN order:

WITH CTE (EmployeeID, FullName, Title, ManagerID) AS
(

SELECT E.EmployeeID, C.FirstName + ' ' + C.LastName FullName, E.Title, E.ManagerID
FROM HumanResources.Employee E
INNER JOIN Person.Contact C ON E.ContactID = C.ContactID
WHERE E.EmployeeID = 3
UNION ALL

SELECT E.EmployeeID, C.FirstName + ' ' + C.LastName FullName, E.Title, E.ManagerID
FROM HumanResources.Employee E
INNER JOIN Person.Contact C ON E.ContactID = C.ContactID
INNER JOIN CTE ON E.EmployeeID = CTE.ManagerID
)

SELECT * FROM CTE

And the employees that the employee (EmployeeID = 3) reports to are:

EmployeeID	Full Name	Title	ManagerID
3	Roberto Tamburello	Engineering Manager	12
12	Terri Duffy	Vice President of Engineering	109
109	Ken Sánchez	Chief Executive Officer	NULL

The post Recursive Queries in SQL Server 2005 appeared first on Blog IT.

Sql Server 2005 Archives - Blog IT

Recursive Queries in SQL Server 2005