Solved

recursive query

Posted on 2011-03-09
4
211 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:ewangoya
ID: 35087033

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

Accepted Solution

by:
ewangoya 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

Free Tool: Postgres Monitoring System

A PHP and Perl based system to collect and display usage statistics from PostgreSQL databases.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

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

Suggested Solutions

PL/SQL can be a very powerful tool for working directly with database tables. Being able to loop will allow you to perform more complex operations, but can be a little tricky to write correctly. This article will provide examples of basic loops alon…
JSON is being used more and more, besides XML, and you surely wanted to parse the data out into SQL instead of doing it in some Javascript. The below function in SQL Server can do the job for you, returning a quick table with the parsed data.
Via a live example, show how to extract information from SQL Server on Database, Connection and Server properties
Via a live example, show how to shrink a transaction log file down to a reasonable size.

827 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