Table valued function using Number List
First I will explain the pieces of code, which form the building blocks of the final table valued function.
We need to create a number list using the CTE as below
;WITH
L0 AS(SELECT 1 AS c UNION ALL SELECT 1),
L1 AS(SELECT 1 AS c FROM L0 AS A, L0 AS B),
L2 AS(SELECT 1 AS c FROM L1 AS A, L1 AS B),
L3 AS(SELECT 1 AS c FROM L2 AS A, L2 AS B),
L4 AS(SELECT 1 AS c FROM L3 AS A, L3 AS B),
Numbers AS(SELECT ROW_NUMBER() OVER(ORDER BY c) AS Number FROM L4)
SELECT * FROM Numbers
This CTE is creating the list of numbers from 1 to POWER(POWER(POWER(POWER(2, 2), 2), 2), 2), i.e. until 65536.
Now Consider the below code snippet, where @list and @delim variables have been assigned.
DECLARE
@list NVARCHAR(MAX), @delim NCHAR(1)
SELECT @list = 'aaa,bbbbb,cccc,dddd', @delim = ','
;WITH
L0 AS(SELECT 1 AS
c UNION ALL SELECT 1),
L1 AS(SELECT 1 AS c FROM L0 AS A, L0 AS B),
L2 AS(SELECT 1 AS c FROM L1 AS A, L1 AS B),
L3 AS(SELECT 1 AS c FROM L2 AS A, L2 AS B),
L4 AS(SELECT 1 AS c FROM L3 AS A, L3 AS B),
Numbers AS(SELECT ROW_NUMBER() OVER(ORDER BY c) AS Number FROM L4)
SELECT
@list List,
SUBSTRING(@list, Number, CHARINDEX(@delim,
@list + @delim, Number) - Number) AS Value,
Number AS StartingFrom,
CHARINDEX(@delim, @list + @delim, Number) AS DelimeterPosition
FROM Numbers
WHERE Number <= CONVERT(INT, LEN(@list))
AND SUBSTRING(@delim + @list, Number,
1) = @delim
The SUBSTRING statement, cuts characters from @list starting from character position (1, 5, 11 and 16).
SUBSTRING(@list, Number, CHARINDEX(@delim, @list + @delim, Number) - Number)
The number of characters to be cut is decided by CHARINDEX which will
return 4, 10, 15, 20 in each row, where it finds the delimiter character.
CHARINDEX(@delim, @list + @delim, Number) - Number
The above SELECT only works until the number of characters present in the
@list variable due to the condition
Number <= CONVERT(INT, LEN(@list))
The duplicate values are filtered out from the output list by the "WHERE" condition created
using the SUBSTRING function which will only return a value when it finds the delimiter
SUBSTRING(@delim + @list, Number, 1) = @delim
The output of the code snippet above would be:
| List |
Value |
Starting From |
Delimiter Position |
| aaa,bbbbb,cccc,dddd | aaa | 1 | 4 |
| aaa,bbbbb,cccc,dddd | bbbbb | 5 | 10 |
| aaa,bbbbb,cccc,dddd | cccc | 11 | 15 |
| aaa,bbbbb,cccc,dddd | dddd | 16 | 20 |
Table valued function using Numbered List: Implementation
Now combining all the above explained pieces of SQL, we create our
table valued function which will parse the string and return a table having two columns viz. ID and Data.
CREATE FUNCTION [dbo].[TableFormDelimetedString]
(
@param NVARCHAR(MAX),
@delimeter NCHAR(1)
)
RETURNS @tmp TABLE
(
ID INT
IDENTITY
(1,
1),
Data Varchar(MAX)
)
BEGIN
;WITH
L0 AS(SELECT 1 AS c UNION ALL SELECT 1),
L1 AS(SELECT 1 AS c FROM L0 AS A, L0 AS B),
L2 AS(SELECT 1 AS c FROM L1 AS A, L1 AS B),
L3 AS(SELECT 1 AS c FROM L2 AS A, L2 AS B),
L4 AS(SELECT 1 AS c FROM L3 AS A, L3 AS B),
Numbers AS(SELECT ROW_NUMBER() OVER(ORDER BY c) AS Number FROM L4)
INSERT INTO
@tmp (Data)
SELECT
LTRIM(RTRIM(CONVERT(NVARCHAR(4000),
SUBSTRING(@param, Number,
CHARINDEX(@delimeter, @param + @delimeter, Number) - Number)
))) AS Value
FROM Numbers
WHERE Number <=
CONVERT(INT, LEN(@param))
AND SUBSTRING(@delimeter+ @param, Number, 1) = @delimeter
RETURN
END
Table valued function using Numbered List: Usage
So if we now invoke the above function like
SELECT * FROM [TableFormDelimetedString]('Andy:Roger:Thomas:Rob:Victor',':')
We will obtain the following result set:
| ID | Data |
| 1 | Andy |
| 2 | Roger |
| 3 | Thomas |
| 4 | Rob |
| 5 | Victor |
Table valued function using recursive CTE
Here again I will first explain the pieces of code,which form
the building blocks of the final table valued function.
As we know, in a recursive CTE, we have one anchor part and one recursive part.
But if we create a CTE having only the anchor part it would look something like
DECLARE
@list NVARCHAR(MAX), @delim NCHAR(1)
SELECT @list = 'aaa,bbbbb,cccc,dddd', @delim
= ','
;WITH CTETable (start, stop) AS
(
SELECT start = CONVERT(bigint, 1), stop = CHARINDEX(@delim, @list +@delim, 1)
)
SELECT @list List, LTRIM(RTRIM(SUBSTRING(@list,
start,
CASE
WHEN
stop > 0
THEN
stop - start
ELSE
0
END
)))
AS Data
start AS StartingFrom, stop
AS DelimiterPosition
FROM CTETable
The output of the SQL above will be like
| List | Value | Starting From | Delimiter Position |
| aaa,bbbbb,cccc,dddd | aaa | 1 | 4 |
Now by adding a recursive member to the above CTE, which iterates over the stop variable, the SQL looks like
DECLARE
@list NVARCHAR(MAX),
@delim NCHAR(1)
SELECT @list = 'aaa,bbbbb,cccc,dddd', @delim = ','
;WITH CTETable (start, stop)
AS
(
SELECT start = CONVERT(bigint, 1), stop = CHARINDEX(@delim, @list +@delim, 1)
UNION ALL -- added for recursive part of CTE
SELECT start = stop + 1, stop = CHARINDEX(@delim, @list +
@delim, stop+ 1) FROM CTETable WHERE
stop > 0 -- added for recursive part of CTE
)
SELECT @list List, LTRIM(RTRIM(SUBSTRING(@list,
start,
CASE
WHEN stop > 0
THEN stop - start
ELSE 0
END
))) AS Data
start AS StartingFrom, stop AS DelimiterPosition
FROM CTETable
WHERE stop > 0
And gives the following result set
| List | Value | Starting From | Delimiter Position |
| aaa,bbbbb,cccc,dddd | aaa | 1 | 4 |
| aaa,bbbbb,cccc,dddd | bbbbb | 5 | 10 |
| aaa,bbbbb,cccc,dddd | cccc | 11 | 15 |
| aaa,bbbbb,cccc,dddd | dddd | 16 | 20 |
Table valued function using recursive CTE: Implementation
Finally we create a table valued function from the above code blocks, which looks like
CREATE FUNCTION [dbo].[TableFormDelimetedStringWithoutNumberList]
(@list NVARCHAR(MAX),
@delim NCHAR(1) = ','
)
RETURNS @tmp TABLE
(
ID INT IDENTITY (1, 1),
Data Varchar(MAX)
)
BEGIN
;WITH CTETable (start, stop)
AS
(
SELECT start = CONVERT(bigint, 1),
stop = CHARINDEX(@delim, @list + @delim)
UNION ALL -- added for recursive part of CTE
SELECT start = stop + 1,
stop = CHARINDEX(@delim, @list + @delim, stop + 1) -- added for recursive part of CTE
FROM CTETable
WHERE stop > 0
)
INSERT INTO @tmp (Data)
SELECT LTRIM(RTRIM(SUBSTRING(@list,
start,
CASE
WHEN stop > 0
THEN
stop - start
ELSE
0
END))) AS Data
FROM CTETable
WHERE stop > 0
RETURN
END
Table valued function using recursive CTE: Usage
So if we now invoke the above function like
SELECT * FROM[TableFormDelimetedStringWithoutNumberList]('Andy:Roger:Thomas:Rob:Victor',':')
We will obtain the following result set:
| ID | Data |
| 1 | Andy |
| 2 | Roger |
| 3 | Thomas |
| 4 | Rob |
| 5 | Victor |
Why I like these two implementations is because the looping has been handled
by the SQL server database engine itself, which would definitely be more efficient
than explicit SQL looping code written by a developer.