Flatten hierarchy

• aaa121

  SSCertifiable

  Points: 5902

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  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?

• ChrisM@Work

  SSC Guru

  Points: 186127

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  December 31, 2013 at 5:11 am

  #1676569

  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/%5B/url%5D

  ^{“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

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  December 31, 2013 at 8:29 am

  #1676597

  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.