Solved

recursive query

Posted on 2011-03-09
4
212 Views
Last Modified: 2012-05-11
How does one write a recursive query?  This would come into play where a table is self-referencing.   Like, a list of employees, where there is a primary Key and supervisor column, where the latter maps to the primary key.   So, If I want a list of employees everyone from person "X" on down, how do I do this?
0
Comment
Question by:HLRosenberger
  • 2
4 Comments
 
LVL 32

Expert Comment

by:Ephraim Wangoya
ID: 35087033

You can use a recursive Common Table Expression (CTE) to do this kind of query
0
 
LVL 32

Accepted Solution

by:
Ephraim Wangoya earned 500 total points
ID: 35087074
here is an example

ID Parent
1  null
2  1
3  1
4  null
5  4
6  5

with CTE(ID, PARENT)
AS
(
      SELECT F.ID, F.PARENT
      FROM TABLE1 F
      WHERE PARENT IS NULL
      UNION ALL
      SELECT F.ID, F.PARENT
      FROM TABLE1 F
      INNER JOIN CTE FH ON FH.ID = F.PARENT
)

SELECT ID, PARENT FROM CTE
0
 
LVL 9

Expert Comment

by:gdupadhyay
ID: 35087209
I believe you are looking to make a tree for employee:
See example below:
ID: Emp ID
Name: Emp Name
Manager: Emp. Manager ID (NULL: Emp. have no manager)

ID      Name      Manager
1      a      NULL
2      b      1
3      c      1
4      X      2
5      Y      2
6      Z      1
7      P      3

WITH Employee_Tree (ID,
		Name,
		Manager,
		Depth) AS(
    SELECT  ID,
		Name,
		Manager,
		1 AS depth
     FROM Employee WITH (NOLOCK)
     WHERE MANAGER IS NULL
   UNION ALL
	SELECT  N.ID,
	        N.Name,
		N.Manager,
		ET.Depth + 1
		FROM Employee AS N WITH (NOLOCK)
	INNER JOIN Employee_Tree ET 
		ON ET.ID = N.Manager)
		SELECT ID,
		   Name,
		   Manager,
	FROM Employee_Tree

Open in new window

0
 
LVL 1

Author Closing Comment

by:HLRosenberger
ID: 35124508
Thanks!
0

Featured Post

Forrester Webinar: xMatters Delivers 261% ROI

Guest speaker Dean Davison, Forrester Principal Consultant, explains how a Fortune 500 communication company using xMatters found these results: Achieved a 261% ROI, Experienced $753,280 in net present value benefits over 3 years and Reduced MTTR by 91% for tier 1 incidents.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

I'm trying, I really am. But I've seen so many wrong approaches involving date(time) boundaries I despair about my inability to explain it. I've seen quite a few recently that define a non-leap year as 364 days, or 366 days and the list goes on. …
I have a large data set and a SSIS package. How can I load this file in multi threading?
Via a live example, show how to extract insert data into a SQL Server database table using the Import/Export option and Bulk Insert.
Via a live example, show how to shrink a transaction log file down to a reasonable size.

713 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question