Find the Nth Occurrence of a Character in a String
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Comments posted to this topic are about the item Find the Nth Occurrence of a Character in a String
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helped me alot, thnx:-)
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I suspect this would be more efficient with a numbers/tally table
declare @TargetStr varchar(8000),@SearchedStr varchar(8000),
@Occurrence int
set @TargetStr='a'
set @SearchedStr='abbabba'
set @Occurrence=3;
WITH Occurrences AS (
SELECT Number,
ROW_NUMBER() OVER(ORDER BY Number) AS Occurrence
FROM master.dbo.spt_values
WHERE Number BETWEEN 1 AND LEN(@SearchedStr) AND type='P'
AND SUBSTRING(@SearchedStr,Number,LEN(@TargetStr))=@TargetStr)
SELECT Number
FROM Occurrences
WHERE Occurrence=@Occurrence
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Deja View - The strange feeling that somewhere, sometime you've optimised this query before
How to get the best help on a forum
http://www.sqlservercentral.com/articles/Best+Practices/61537
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Looks wrong, if you go more than 1 above the maximum char number then it will loop through again.
if you change the WHILE statement from
while (@counter < @Occurrence)to
while (@counter < @Occurrence) and @pos <> 0that should fix the issueTry running below
DECLARE @TXT varchar(255)
SET @TXT = 'Michael Williamson'
SELECT dbo.CHARINDEX2('l',@TXT,1)
SELECT dbo.CHARINDEX2('l',@TXT,2)
SELECT dbo.CHARINDEX2('l',@TXT,4)
SELECT dbo.CHARINDEX2('l',@TXT,6)
Hope that helps
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Thanks! I found this function really useful. Just adding the middle line here got around the looping issue for me:
set @pos = @ret
if @pos = 0 set @counter = @Occurrence
end
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Thank you for your fix code! I was banging my head agains the wall to find out why my stored proc was bugging out sometimes - turns out that one of my functions was using this charindex2 without accounting for looping behavior
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This is an old thread but I would suggest a different approach. It might get give better results performance wise.
/*
Example:
SELECT dbo.CHARINDEX2('a', 'abbabba', 3)
returns the location of the third occurrence of 'a'
which is 7
*/
CREATE FUNCTION [dbo].[ProperCase]
(
@TargetStr CHAR(1),
@SearchedStr VARCHAR(8000),
@Occurrence INT = 2
)
RETURNS TABLE WITH SCHEMABINDING AS
RETURN
--===== "Inline" CTE Driven "Tally Table" produces values from 0 up to 10,000...
-- enough to cover VARCHAR(8000)
WITH E1(N) AS (
SELECT N FROM (VALUES(1),(1),(1),(1),(1),(1),(1),(1),(1),(1))x(N)
), --10E+1 or 10 rows
E2(N) AS (SELECT 1 FROM E1 a, E1 b), --10E+2 or 100 rows
E4(N) AS (SELECT 1 FROM E2 a, E2 b), --10E+4 or 10,000 rows max
cteTally(N) AS (--==== This provides the "base" CTE and limits the number of rows right up front
-- for both a performance gain and prevention of accidental "overruns"
SELECT TOP (ISNULL(DATALENGTH(@SearchedStr),0)) ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) FROM E4
),
cteAppearances(N, rn) AS( SELECT N, ROW_NUMBER() OVER (ORDER BY N) rn
FROM cteTally
WHERE SUBSTRING(@SearchedStr, N, 1) = @TargetStr
)
SELECT TOP 1 CASE WHEN rn >= @Occurrence THEN N ELSE 0 END N
FROM cteAppearances
WHERE rn = @Occurrence OR rn < @Occurrence
ORDER BY N DESC
GO
/*
Example:
SELECT dbo.CHARINDEX2('a', 'abbabba', 3)
returns the location of the third occurrence of 'a'
which is 7
*/
CREATE FUNCTION [dbo].[ProperCase2]
(
@TargetStr VARCHAR(8000),
@SearchedStr VARCHAR(8000),
@Occurrence INT = 2
)
RETURNS TABLE WITH SCHEMABINDING AS
RETURN
--===== "Inline" CTE Driven "Tally Table" produces values from 0 up to 10,000...
-- enough to cover VARCHAR(8000)
WITH E1(N) AS (
SELECT N FROM (VALUES(1),(1),(1),(1),(1),(1),(1),(1),(1),(1))x(N)
), --10E+1 or 10 rows
E2(N) AS (SELECT 1 FROM E1 a, E1 b), --10E+2 or 100 rows
E4(N) AS (SELECT 1 FROM E2 a, E2 b), --10E+4 or 10,000 rows max
cteTally(N) AS (--==== This provides the "base" CTE and limits the number of rows right up front
-- for both a performance gain and prevention of accidental "overruns"
SELECT TOP (ISNULL(DATALENGTH(@SearchedStr),0)) ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) FROM E4
),
cteAppearances(N, rn) AS( SELECT N, ROW_NUMBER() OVER (ORDER BY N) rn
FROM cteTally
WHERE SUBSTRING(@SearchedStr, N, LEN(@TargetStr)) = @TargetStr
)
SELECT TOP 1 CASE WHEN rn >= @Occurrence THEN N ELSE 0 END N
FROM cteAppearances
WHERE rn = @Occurrence OR rn < @Occurrence
ORDER BY N DESC
GO
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Hello!
I am using charindex2 at the moment.
Since I have rows with more than 8000 characters, i've changed these two from (8000) to (max):
@TargetStr varchar(8000),
@SearchedStr varchar(8000)While both fixes:
while (@counter < @Occurrence) and @pos <> 0
and:
if @pos = 0 set @counter = @Occurrence
prevents looping of whole dataset, it doesn't prevent first instance to loop forever.Example:
I have: 'a,b,c,d,e'
I want to put that into table with say 8 rows, like this: 'a','b','c','d','e','','',''
Without any of the above, it gives me this: 'a','b','c','d','e','a','b','c'
But with either (or even both), it gives me this: 'a','b','c','d','e','a','a','a'I presume it's something elementary, but I'm not seeing it.
I am using SQL Server 2014 Express.
Thank you!
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