• WayneS (6/28/2010)


    lmu92 (6/28/2010)


    This thread include a post by WayneS showing the DelimitedSplit8K function I'm using at the moment.

    I believe I saw a follow-up post from Jeff where he found that the UNPIVOT (as demonstrated in the above link) turns out to be slower when he ran it on his work prod server several times. Jeff, please let us know if I remember this correctly.

    You did, indeed. I didn't take the time to analyze "why" but on certain machines with multiple processors, the UNPIVOT method sometimes runs substantially slower. I also didn't understand that the function you good folks were talking about was the function that I posted. Here's the latest and greatest with all the documentation and optimizations that I currently use for production code... the documentation in the header is quite substantial. {EDIT} Updated the code below to include the lastest performance (From yesterday) thanks to Paul White.

    CREATE FUNCTION dbo.DelimitedSplit8K

    /***************************************************************************************************

    Purpose:

    Split a given string at a given delimiter and return a list of the split elements (items).

    Returns:

    iTVF containing the following:

    ItemNumber = Element position of Item as a BIGINT (not converted to INT to eliminate a CAST)

    Item = Element value as a VARCHAR(8000)

    CROSS APPLY Usage Example:

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

    --===== Conditionally drop the test tables to make reruns easier for testing.

    -- (this is NOT a part of the solution)

    IF OBJECT_ID('tempdb..#JBMTest') IS NOT NULL

    DROP TABLE #JBMTest

    ;

    --===== Create and populate a test table on the fly (this is NOT a part of the solution).

    SELECT *

    INTO #JBMTest

    FROM (

    SELECT 1,'1,10,100,1000,10000,100000,1000000' UNION ALL

    SELECT 2,'2000000,200000,20000,2000,200,20,2' UNION ALL

    SELECT 3, 'This,is,a,test' UNION ALL

    SELECT 4, 'and so is this' UNION ALL

    SELECT 5, 'This, too (no pun intended)'

    ) d (SomeID,SomeValue)

    ;

    GO

    --===== Split the CSV column for the whole table using CROSS APPLY (this is the solution)

    SELECT test.SomeID, split.ItemNumber, split.Item

    FROM #JBMTest test

    CROSS APPLY

    (

    SELECT ItemNumber, Item

    FROM dbo.DelimitedSplit8k(test.SomeValue,',')

    ) split

    ;

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

    Notes:

    1. Optimized for VARCHAR(7999) or less. No testing or error reporting for truncation at 7999

    characters is done.

    2. Optimized for single character delimiter. Multi-character delimiters should be resolved

    externally from this function.

    3. Optimized for use with CROSS APPLY.

    4. Does not "trim" elements just in case leading or trailing blanks are intended.

    5. If you don't know how a Tally table can be used to replace loops, please see the following...

    http://www.sqlservercentral.com/articles/T-SQL/62867/

    6. Changing this function to use VARCHAR(MAX) will cause it to run twice as slow. It's just the

    nature of VARCHAR(MAX) whether it fits in-row or not.

    7. Multi-machine testing for the method of using UNPIVOT instead of 10 SELECT/UNION ALLs shows

    that the UNPIVOT method is quite machine dependent and can slow things down quite a bit.

    8. Performance testing shows using "TOP" for the limiting criteria of "N" is actually

    slower and slightly more CPU intensive than the traditional WHERE N < LEN(@pString) + 2.

    9. Performance testing shows using ORDER BY (SELECT x) where "x" is anything is actually

    slower and slightly more CPU intensive than the traditional ORDER BY (SELECT N).

    Credits:

    This code is the product of many people's efforts including but not limited to the following:

    cteTally concept originally by Iztek Ben Gan and "decimalized" by Lynn Pettis (and others) for a

    bit of extra speed and finally redacted by Jeff Moden for a different slant on readability and

    compactness. Hat's off to Paul White for his simple explanations of CROSS APPLY. Finally,

    special thanks to Erland Sommarskog for his tireless efforts to help people understand

    what you can actually do with T-SQL. I also thank whoever wrote the first article I ever saw

    on "numbers tables" which is located at the following URL ...

    http://sqlserver2000.databases.aspfaq.com/why-should-i-consider-using-an-auxiliary-numbers-table.html

    Revision History:

    Rev 00 - 20 Jan 2010 - Concept: Lynn Pettis and others.

    Redaction/Implementation: Jeff Moden

    - Base 10 redaction and reduction for CTE. (Total rewrite)

    Rev 01 - 13 Mar 2010 - Jeff Moden

    - Removed one additional concatenation and one subtraction from the SUBSTRING in the

    SELECT List for that tiny bit of extra speed.

    Rev 02 - 14 Apr 2010 - Jeff Moden

    - No code changes. Added CROSS APPLY usage example to the header, some additional credits,

    and extra documentation.

    Rev 03 - 18 Apr 2010 - Jeff Moden

    - No code changes. Added notes 7, 8, and 9 about certain "optimizations" that dont'

    actually work for this type of function.

    Rev 04 - 29 Jun 2010 - Jeff Moden

    - Added WITH SCHEMABINDING thanks to a note by Paul White. This prevents an unnecessary

    "Table Spool" when the function is used in an UPDATE statement even though the function

    makes no external references.

    ***************************************************************************************************/

    --===== Define I/O parameters

    (

    @pString VARCHAR(7999),

    @pDelimiter CHAR(1)

    )

    RETURNS TABLE

    WITH SCHEMABINDING

    AS

    RETURN

    --===== "Inline" CTE Driven "Tally Table” produces values up to

    -- 10,000... enough to cover VARCHAR(8000)

    WITH

    E1(N) AS ( --=== Create Ten 1's

    SELECT 1 UNION ALL SELECT 1 UNION ALL

    SELECT 1 UNION ALL SELECT 1 UNION ALL

    SELECT 1 UNION ALL SELECT 1 UNION ALL

    SELECT 1 UNION ALL SELECT 1 UNION ALL

    SELECT 1 UNION ALL SELECT 1 --10

    ),

    E2(N) AS (SELECT 1 FROM E1 a, E1 b), --100

    E4(N) AS (SELECT 1 FROM E2 a, E2 b), --10,000

    cteTally(N) AS (SELECT ROW_NUMBER() OVER (ORDER BY (SELECT N)) FROM E4)

    --===== Do the split

    SELECT ROW_NUMBER() OVER (ORDER BY N) AS ItemNumber,

    SUBSTRING(@pString, N, CHARINDEX(@pDelimiter, @pString + @pDelimiter, N) - N) AS Item

    FROM cteTally

    WHERE N < LEN(@pString) + 2

    AND SUBSTRING(@pDelimiter + @pString, N, 1) = @pDelimiter

    ;

    GO

    --Jeff Moden


    RBAR is pronounced "ree-bar" and is a "Modenism" for Row-By-Agonizing-Row.
    First step towards the paradigm shift of writing Set Based code:
    ________Stop thinking about what you want to do to a ROW... think, instead, of what you want to do to a COLUMN.
    "Change is inevitable... change for the better is not".
    "Dear Lord... I'm a DBA so please give me patience because, if you give me strength, I'm going to need bail money too!"

    Helpful Links:
    How to post code problems
    How to Post Performance Problems
    Create a Tally Function (fnTally)