Flatten hierarchy

Question

Post reply

Flatten hierarchy

aaa121

SSCertifiable

Points: 5902
More actions
December 31, 2013 at 3:54 am

#286681

I know there have been several forum discussions about flattening hierarchies using recursive CTEs but the examples I have found have a ParentID field in the data. My data does not have this.
Please take a look at this sample code
declare @table table
(id varchar(10),
levelid int,
leveldesc varchar(250))
insert into @table
select 'DP961A1111', 1, 'LevelDesc1'
union
select 'DP961A1111', 2, 'LevelDesc2'
union
select 'DP961A1111', 3, 'LevelDesc3'
select * from @table
--I need to display the results like this:
select 'DP961A1111' as id, 'LevelDesc1' as LevelDesc1, 'LevelDesc2' as LevelDesc2, 'LevelDesc3' as LevelDesc3
Can you guys help?

Viewing 3 posts - 1 through 2 (of 2 total)

You must be logged in to reply to this topic. Login to reply

ChrisM@Work SSC Guru Points: 186127 More actions · Answer 1

Try this - it's called a CROSSTAB query:

SELECT id,

LevelDesc1 = MAX(CASE WHEN levelid = 1 THEN leveldesc ELSE NULL END),

LevelDesc2 = MAX(CASE WHEN levelid = 2 THEN leveldesc ELSE NULL END),

LevelDesc3 = MAX(CASE WHEN levelid = 3 THEN leveldesc ELSE NULL END)

FROM @table

GROUP BY id

Here's a great article to explain how it works, and how far you can go with it:

http://www.sqlservercentral.com/articles/T-SQL/63681/[/url]

^{“Write the query the simplest way. If through testing it becomes clear that the performance is inadequate, consider alternative query forms.” - Gail Shaw}

For fast, accurate and documented assistance in answering your questions, please read this article.
Understanding and using APPLY, (I) and (II) Paul White
Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden

aaa121 SSCertifiable Points: 5902 More actions · Answer 2

I have came across the crosstab query before but only in theory, never used it in anger! I'll give this a go.

Thanks for your help, greatly appreciated.