Check a chunk of text for tilde and ensure they are 60 characters apart. If not place a tilde inbetween - sql

Question

I currently have a function in SQL that places a tilde every 60 characters, but the original text already has tilde's so , basically I want to change that if there is a tilde and the next tilde is under 60 characters away, then skip to the next tilde. If its over 60 characters, then only then place a extra tilde.
My current function looks like;
function [dbo].[AddTilde] (
#string varchar(max),
#count int
)
returns varchar(max)
as
begin
declare #result varchar(max) = ''
declare #token varchar(max) = ''
while DATALENGTH(#string) > 0
begin
select #token = left(#string, #count)
select #string = REPLACE(#string, #token, '')
select #result +=#token +case when DATALENGTH(#string)=0 then '' else '~' end
end
return #result
end
Any help appreciated
Many Thanks

Answer 1

DECLARE #string1 VARCHAR(max),
#string2 VARCHAR(max) = '',
#i1 INT,
#i2 INT
SET #string1 = '12345678901234567890~1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890'
WHILE LEN(#string1) > 0
BEGIN
SET #i1 = CHARINDEX('~',#string1)
SET #i2 = #i1 - (ABS(#i1-60) + (#i1-60)) / 2 -- MINIMUM OF ~ LOCATION AND 60
SET #i1 = LEN(#string1)
IF #i2 = 0 SET #i2 = #i1 - (ABS(#i1-60) + (#i1-60)) / 2 -- MINIMUM OF LENGTH OF #string1 LOCATION AND 60
IF #i2 < 60
BEGIN
SET #string2 = #string2 + LEFT(#string1,#i2)
SET #string1 = RIGHT(#string1,#i1-#i2)
END
ELSE
BEGIN
SET #string2 = #string2 + LEFT(#string1,60) + '~'
SET #string1 = RIGHT(#string1,#i1-60)
END
END
Results: 12345678901234567890~123456789012345678901234567890123456789012345678901234567890~1234567890123456789012345678901234567890

Answer 2

This is based on my String Splitting function, which has a very good performance.
This function should be quite efficient, albeit hard to understand (I have added a few commenets in attempt to make it easier).
You can change internal parameters easily e.g. #Delimitor can be multiple characters
Test cases are included at the bottom.
ALTER FUNCTION [dbo].[AddTilde]
(
#String VARCHAR( MAX ),
#Count INT
)
RETURNS VARCHAR(MAX)
AS
BEGIN
DECLARE #CurrentPosition BIGINT, #NextDelimiterPosition BIGINT, #NextFixedPosition BIGINT, #NextPosition BIGINT,
#DelimiterLength INT, #Delimiter VARCHAR( 5 ), #Result VARCHAR( MAX )
-- Initialise
SET #Delimiter = '~'
SET #DelimiterLength = LEN( #Delimiter )
SET #Result = ''
-- Ensures we can terminate loop without using an extra IF condition, saves a few = 0 checks
SET #String = #String + #Delimiter
SET #CurrentPosition = 1
-- Check for next Tilde position
SET #NextDelimiterPosition = CHARINDEX( #Delimiter, #String, #CurrentPosition )
-- Initialise fixed increment position
SET #NextFixedPosition = #Count
-- Compare, which one is earlier and use that one. Handle cases where the next token begins with Tilde
SET #NextPosition = CASE WHEN #NextDelimiterPosition - #DelimiterLength > #NextFixedPosition THEN #NextFixedPosition ELSE #NextDelimiterPosition END
WHILE #NextDelimiterPosition > 0
BEGIN
SET #Result = #Result + SUBSTRING( #String, #CurrentPosition, #NextPosition - #CurrentPosition + 1 )
-- Handle cases where the next token begins with Tilde and avoids doubling up Tildes
+ ( CASE WHEN #NextPosition = #NextDelimiterPosition THEN '' ELSE #Delimiter END )
SET #CurrentPosition = #NextPosition + 1
-- Increment fixed position
SET #NextFixedPosition = #CurrentPosition + #Count - 1
-- Check for next Tilde position
SET #NextDelimiterPosition = CHARINDEX( #Delimiter, #String, #CurrentPosition )
SET #NextPosition = CASE WHEN #NextDelimiterPosition - #DelimiterLength > #NextFixedPosition THEN #NextFixedPosition ELSE #NextDelimiterPosition END
END
-- Remove trailing Tilde
SET #Result = SUBSTRING( #Result, 1, LEN( #Result ) - #DelimiterLength )
RETURN #Result
END
/* Test Cases
SELECT dbo.[AddTilde]( 'ab~c~defghijkl~', 3 ) --> 'ab~c~def~ghi~jkl~'
SELECT dbo.[AddTilde]( '~ab~c~defghijkl', 3 ) --> '~ab~c~def~ghi~jkl'
SELECT dbo.[AddTilde]( 'ab~c~~defghijkl', 3 ) --> 'ab~c~~def~ghi~jkl'
SELECT dbo.[AddTilde]( 'abcdefghijkl', 3 ) --> 'abc~def~ghi~jkl'
SELECT dbo.[AddTilde]( 'a', 3 ) --> 'a'
*/