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TSQL for Table-Valued Function

Posted on 2015-01-19
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Last Modified: 2015-01-20
What does the following part ctually perform ??

#1  
  WITH Split(stpos,endpos)
    AS(
        SELECT 0 AS stpos, CHARINDEX(@Delimiter,@String) AS endpos
        UNION ALL
        SELECT endpos+1, CHARINDEX(@Delimiter,@String,endpos+1)
            FROM Split
            WHERE endpos > 0
    )

#2
    SELECT 'Id' = ROW_NUMBER() OVER (ORDER BY (SELECT 1)),

#3
        'Data' = SUBSTRING(@String,stpos,COALESCE(NULLIF(endpos,0),LEN(@String)+1)-stpos)


------------------------------------------------------
CREATE FUNCTION [dbo].[Split]
(
    @String NVARCHAR(4000),
    @Delimiter NCHAR(1)
)
RETURNS TABLE
AS
RETURN
(
    WITH Split(stpos,endpos)
    AS(
        SELECT 0 AS stpos, CHARINDEX(@Delimiter,@String) AS endpos
        UNION ALL
        SELECT endpos+1, CHARINDEX(@Delimiter,@String,endpos+1)
            FROM Split
            WHERE endpos > 0
    )
    SELECT 'Id' = ROW_NUMBER() OVER (ORDER BY (SELECT 1)),
        'Data' = SUBSTRING(@String,stpos,COALESCE(NULLIF(endpos,0),LEN(@String)+1)-stpos)
    FROM Split
)
GO
0
Comment
Question by:AXISHK
  • 3
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8 Comments
 
LVL 24

Expert Comment

by:Phillip Burton
Comment Utility
#1 is a CTE. It splits the first string into separate rows based on the second string, and gives the position of the start of the split and the end.

#2 identifies the row number. The OVER(ORDER BY (SELECT 1)) is because you have to put something in the OVER, and that just means "I don't care about the order".

#3 converts the positions identified in #1 and creates the actual strings based on those positions.
0
 

Author Comment

by:AXISHK
Comment Utility
Tks, still have problem,

Function name is "Split', select table name is 'Split'. Is the function calling itself recursively ??

Tks
0
 
LVL 24

Expert Comment

by:Phillip Burton
Comment Utility
No - Split is different to dbo.split.

You could change

 WITH Split(stpos,endpos)
...
            FROM Split
...
    FROM Split

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to

 WITH Hello(stpos,endpos)
...
            FROM Hello
...
    FROM Hello

Open in new window


and still get the right answer.

The fact that the function is called dbo.Split doesn't make any difference.
0
 
LVL 48

Expert Comment

by:PortletPaul
Comment Utility
>>"#1 is a CTE" (?)

a CTE is a "Common Table Expression"
Specifies a temporary named result set, known as a common table expression (CTE). This is derived from a simple query and defined within the execution scope of a single SELECT, INSERT, UPDATE, or DELETE statement.
http://msdn.microsoft.com/en-AU/library/ms175972.aspx

No points please.
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LVL 48

Expert Comment

by:PortletPaul
Comment Utility
>>" Is the function calling itself recursively ??"

The function is not being called recursively, but the CTE is calling itself recursively (which is allowed)
... A common table expression can include references to itself. This is referred to as a recursive common table expression.
http://msdn.microsoft.com/en-AU/library/ms175972.aspx

No points please.
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Author Comment

by:AXISHK
Comment Utility
I can't get the idea  in #1

select 0 as stops, CHARINDEX(',' , 'Duckman, Cornfed, Ajax, Charles, Mambo') AS endpos       

it will return :
stops     endpos
0             8
About the second one, how does it iterate from the Split  ? can I stimulate it in Management Studio ? Tks
        SELECT endpos+1, CHARINDEX(@Delimiter,@String,endpos+1)
             FROM Split
             WHERE endpos > 0
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Assisted Solution

by:Phillip Burton
Phillip Burton earned 200 total points
Comment Utility
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Accepted Solution

by:
PortletPaul earned 300 total points
Comment Utility
?... Typically one introduces the full name then resorts to the abbreviation.
---------------
For this recursive CTE:

{+edit} Don't forget that the CHARINDEX() function uses the optional third parameter to establish where to start from. This increases at each iteration.

On the first iteration
select 0 as stops, CHARINDEX(',' , 'Duckman, Cornfed, Ajax, Charles, Mambo') AS endpos      
it will return :
stops     endpos
0             8
It then enters the second iteration
SELECT endpos+1, CHARINDEX(',' , 'Duckman, Cornfed, Ajax, Charles, Mambo',endpos+1) AS endpos  
which returns
stops     endpos
9             17           -- the comma after Cornfed
It then enters the third iteration
SELECT endpos+1, CHARINDEX(',' , 'Duckman, Cornfed, Ajax, Charles, Mambo',endpos+1) AS endpos  
which returns
stops     endpos
18             23           -- the comma after Ajax
It then enters the fourth iteration
SELECT endpos+1, CHARINDEX(',' , 'Duckman, Cornfed, Ajax, Charles, Mambo',endpos+1) AS endpos  
which returns
stops     endpos
24             32           -- the comma after Charles
It then enters the fifth iteration
SELECT endpos+1, CHARINDEX(',' , 'Duckman, Cornfed, Ajax, Charles, Mambo',endpos+1) AS endpos  
which returns
stops     endpos
33             0           -- there is no comma after position 33 of the string
Now the endpos is zero the iterations stop due to the where clause:

             WHERE endpos > 0

You can run this as a query to see the effect.
declare @String NVARCHAR(4000) = 'Duckman, Cornfed, Ajax, Charles, Mambo'
declare @Delimiter NCHAR(1) = ','

    ;WITH Split(stpos,endpos)
    AS(
        SELECT 0 AS stpos, CHARINDEX(@Delimiter,@String) AS endpos
        UNION ALL
        SELECT endpos+1, CHARINDEX(@Delimiter,@String,endpos+1)
            FROM Split
            WHERE endpos > 0
    )
    SELECT
        'Id' = ROW_NUMBER() OVER (ORDER BY (SELECT 1)),
        'Data' = SUBSTRING(@String,stpos,COALESCE(NULLIF(endpos,0),LEN(@String)+1)-stpos)
      , stpos
      , endpos
    FROM Split

Open in new window

which produces:
| ID |     DATA | STPOS | ENDPOS |
|----|----------|-------|--------|
|  1 |  Duckman |     0 |      8 |
|  2 |  Cornfed |     9 |     17 |
|  3 |     Ajax |    18 |     23 |
|  4 |  Charles |    24 |     32 |
|  5 |    Mambo |    33 |      0 |

Open in new window

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