How this works?

• vignesh.ms

  Hall of Fame

  Points: 3456

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  July 24, 2014 at 8:11 am

  #293692

  Hi there ,

  I got this code from web, I cant understand how it works

  can anybody suggest me with links or explanations about the below used techniques.

  DECLARE @t TABLE( ID INT IDENTITY, data VARCHAR(20))

  INSERT INTO @t(data) SELECT 'Jacob'

  INSERT INTO @t(data) SELECT 'Sebastian'

  ;WITH Numbers(N) AS (

  SELECT DISTINCT Number

  FROM master..spt_values

  WHERE Number BETWEEN 1 AND (SELECT MAX(LEN(data))FROM @t)

  )

  SELECT

  id,

  data_reversed

  FROM @t T1

  CROSS APPLY(

  SELECT

  SUBSTRING(data,N,1)

  FROM @t T2 JOIN Numbers ON N<=LEN(data)

  WHERE T1.id=T2.id

  ORDER BY N DESC

  FOR XML PATH('')

  )x(data_reversed)

  ORDER BY id DESC

• ChrisM@Work

  SSC Guru

  Points: 186127

  More actions

  July 24, 2014 at 8:29 am

  #1732108

  -- make a table with two rows, two columns

  DECLARE @t TABLE( ID INT IDENTITY, data VARCHAR(20))

  INSERT INTO @t(data) SELECT 'Jacob'

  INSERT INTO @t(data) SELECT 'Sebastian'

  SELECT * FROM @t

  GO

  ----------------------------------------------------------------------------------------------------

  DECLARE @t TABLE( ID INT IDENTITY, data VARCHAR(20))

  INSERT INTO @t(data) SELECT 'Jacob'

  INSERT INTO @t(data) SELECT 'Sebastian'

  -- a CTE which provides n rows containing values 1 through n,

  -- where n is the longest word in column [data]

  SELECT DISTINCT Number

  FROM master..spt_values

  WHERE Number BETWEEN 1 AND (SELECT MAX(LEN(data))FROM @t)

  GO

  ----------------------------------------------------------------------------------------------------

  DECLARE @t TABLE( ID INT IDENTITY, data VARCHAR(20))

  INSERT INTO @t(data) SELECT 'Jacob'

  INSERT INTO @t(data) SELECT 'Sebastian'

  -- pick the letters from [data] one by one, putting each one on a separate row of the output

  ;WITH Numbers(N) AS (

  SELECT DISTINCT Number

  FROM master..spt_values

  WHERE Number BETWEEN 1 AND (SELECT MAX(LEN(data))FROM @t)

  )

  SELECT T2.id, N,

  SUBSTRING(data,N,1)

  FROM @t T2 JOIN Numbers ON N<=LEN(data)

  --WHERE T1.id=T2.id

  ORDER BY T2.id, N DESC -- added T2.id for clarity

  --FOR XML PATH('')

  GO

  ----------------------------------------------------------------------------------------------------

  -- finally, FOR XML PATH concatenates the values from each row (for each id)

  -- ORDER BY N DESC ensures that the letters are concatenated in the reverse order from collection.

  DECLARE @t TABLE( ID INT IDENTITY, data VARCHAR(20))

  INSERT INTO @t(data) SELECT 'Jacob'

  INSERT INTO @t(data) SELECT 'Sebastian'

  ;WITH Numbers(N) AS (

  SELECT DISTINCT Number

  FROM master..spt_values

  WHERE Number BETWEEN 1 AND (SELECT MAX(LEN(data))FROM @t)

  )

  SELECT

  id,

  data_reversed

  FROM @t T1

  CROSS APPLY(

  SELECT

  SUBSTRING(data,N,1)

  FROM @t T2 JOIN Numbers ON N<=LEN(data)

  WHERE T1.id=T2.id

  ORDER BY N DESC

  FOR XML PATH('')

  )x(data_reversed)

  ORDER BY id DESC

  ----------------------------------------------------------------------------------------------------

  ^{“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

• ChrisM@Work

  SSC Guru

  Points: 186127

  More actions

  July 24, 2014 at 8:30 am

  #1732110

  vignesh.ms (7/24/2014)

  ---

  Hi there ,

  I got this code from web, I cant understand how it works

  can anybody suggest me with links or explanations about the below used techniques.

  .

  .

  .

  An excellent article here[/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

• Luis Cazares

  SSC Guru

  Points: 183698

  More actions

  July 24, 2014 at 8:37 am

  #1732113

  I hope that you're using that code for learning purposes only and not instead of REVERSE() function.

  Luis C.
  General Disclaimer:
  Are you seriously taking the advice and code from someone from the internet without testing it? Do you at least understand it? Or can it easily kill your server?

  How to post data/code on a forum to get the best help: Option 1 / Option 2

• vignesh.ms

  Hall of Fame

  Points: 3456

  More actions

  July 25, 2014 at 4:12 am

  #1732306

  Luis Cazares (7/24/2014)

  ---

  I hope that you're using that code for learning purposes only and not instead of REVERSE() function.

  yes of course

• vignesh.ms

  Hall of Fame

  Points: 3456

  More actions

  July 25, 2014 at 4:34 am

  #1732309

  ChrisM@Work (7/24/2014)

  ---

  -- make a table with two rows, two columns

  DECLARE @t TABLE( ID INT IDENTITY, data VARCHAR(20))

  INSERT INTO @t(data) SELECT 'Jacob'

  INSERT INTO @t(data) SELECT 'Sebastian'

  SELECT * FROM @t

  GO

  ----------------------------------------------------------------------------------------------------

  DECLARE @t TABLE( ID INT IDENTITY, data VARCHAR(20))

  INSERT INTO @t(data) SELECT 'Jacob'

  INSERT INTO @t(data) SELECT 'Sebastian'

  -- a CTE which provides n rows containing values 1 through n,

  -- where n is the longest word in column [data]

  SELECT DISTINCT Number

  FROM master..spt_values

  WHERE Number BETWEEN 1 AND (SELECT MAX(LEN(data))FROM @t)

  GO

  ----------------------------------------------------------------------------------------------------

  DECLARE @t TABLE( ID INT IDENTITY, data VARCHAR(20))

  INSERT INTO @t(data) SELECT 'Jacob'

  INSERT INTO @t(data) SELECT 'Sebastian'

  -- pick the letters from [data] one by one, putting each one on a separate row of the output

  ;WITH Numbers(N) AS (

  SELECT DISTINCT Number

  FROM master..spt_values

  WHERE Number BETWEEN 1 AND (SELECT MAX(LEN(data))FROM @t)

  )

  SELECT T2.id, N,

  SUBSTRING(data,N,1)

  FROM @t T2 JOIN Numbers ON N<=LEN(data)

  --WHERE T1.id=T2.id

  ORDER BY T2.id, N DESC -- added T2.id for clarity

  --FOR XML PATH('')

  GO

  ----------------------------------------------------------------------------------------------------

  -- finally, FOR XML PATH concatenates the values from each row (for each id)

  -- ORDER BY N DESC ensures that the letters are concatenated in the reverse order from collection.

  DECLARE @t TABLE( ID INT IDENTITY, data VARCHAR(20))

  INSERT INTO @t(data) SELECT 'Jacob'

  INSERT INTO @t(data) SELECT 'Sebastian'

  ;WITH Numbers(N) AS (

  SELECT DISTINCT Number

  FROM master..spt_values

  WHERE Number BETWEEN 1 AND (SELECT MAX(LEN(data))FROM @t)

  )

  SELECT

  id,

  data_reversed

  FROM @t T1

  CROSS APPLY(

  SELECT

  SUBSTRING(data,N,1)

  FROM @t T2 JOIN Numbers ON N<=LEN(data)

  WHERE T1.id=T2.id

  ORDER BY N DESC

  FOR XML PATH('')

  )x(data_reversed)

  ORDER BY id DESC

  ----------------------------------------------------------------------------------------------------

  Good explanation...

  Splitting query into chunks make me understand easily. Really its very useful to me. Thanks for your time & effort..