Function for String Occurences Count

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Function for String Occurences Count

ece.viky

Right there with Babe

Points: 727
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December 30, 2014 at 11:18 am

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Comments posted to this topic are about the item Function for String Occurences Count

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erlend.miller 3298 Valued Member Points: 57 More actions · Answer 1

Nice but can't help but feel it's overcomplicating it a bit. What about:

DECLARE @ReturnValue AS INT

SET @ReturnValue = 0

IF LEN(@SearchString) > 0

BEGIN

SET @ReturnValue = (LEN(@InputString) - LEN(REPLACE(@InputString,@SearchString,''))) / LEN(@SearchString)

END

RETURN @ReturnValue

ece.viky Right there with Babe Points: 727 More actions · Answer 2

Great.....Super modification...Thanks for your input........

Alan Knepper SSC Journeyman Points: 96 More actions · Answer 3

erlend.miller 3298 - I love the simplicity of your approach! What if we add COALESCE(NULLIF()) to the calculation to take care of the potential divide by zero error if the @SearchString is passed in as an empty string? This eliminates the need for the IF statement and further simplifies your solution. In practice we would want to handle NULLs being passed into the parameters. Expanding on your solution, here is how we can pull it all together in a function that I will be adding to my SQL toolbox. Thanks!

IF EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[fn_get_string_occurrences_count]') AND type in (N'FN', N'IF', N'TF', N'FS', N'FT'))

DROP FUNCTION [dbo].[fn_get_string_occurrences_count]

GO

CREATE FUNCTION dbo.fn_get_string_occurrences_count

(

@InputString VARCHAR(MAX),

@SearchString VARCHAR(256)

)

RETURNS INT

AS

BEGIN

RETURN (LEN(COALESCE(@InputString, ''))

- LEN(REPLACE(COALESCE(@InputString, ''), COALESCE(@SearchString, ''), '')))

/ LEN(COALESCE(NULLIF(@SearchString,''), 'X'))

END

GO

akljfhnlaflkj SSC Guru Points: 76202 More actions · Answer 4

Thanks. I think I may have something to actually use this on.

Alan Burstein SSC Guru Points: 61141 More actions · Answer 5

You can use NGrams8K for a set-based way of solving this kind of thing.

The function:

CREATE FUNCTION dbo.NGrams8k

(

@string varchar(8000), -- Input string

@N int -- requested token size

)

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

Purpose:

A character-level @N-Grams function that outputs a contiguous stream of @N-sized tokens

based on an input string (@string). Accepts strings up to 8000 varchar characters long.

For more information about N-Grams see: http://en.wikipedia.org/wiki/N-gram.

Compatibility:

SQL Server 2008+ and Azure SQL Database

Syntax:

--===== Autonomous

SELECT position, token FROM dbo.NGrams8k(@string,@N);

--===== Against a table using APPLY

SELECT s.SomeID, ng.position, ng.string

FROM dbo.SomeTable s

CROSS APPLY dbo.NGrams8K(s.SomeValue,@N) ng;

Parameters:

@string = The input string to split into tokens.

@N = The size of each token returned.

Returns:

Position = bigint; the position of the token in the input string

token = varchar(8000); a @N-sized character-level N-Gram token

Examples:

--===== Turn the string, 'abcd' into unigrams, bigrams and trigrams

SELECT position, token FROM dbo.NGrams8k('abcd',1); -- unigrams (@N=1)

SELECT position, token FROM dbo.NGrams8k('abcd',2); -- bigrams (@N=2)

SELECT position, token FROM dbo.NGrams8k('abcd',3); -- trigrams (@N=1)

--===== How many times the substring "AB" appears in each record

DECLARE @table TABLE(stringID int identity primary key, string varchar(100));

INSERT @table(string) VALUES ('AB123AB'),('123ABABAB'),('!AB!AB!'),('AB-AB-AB-AB-AB');

SELECT string, occurances = COUNT(*)

FROM @table t

CROSS APPLY dbo.NGrams8k(t.string,2) ng

WHERE ng.token = 'AB'

GROUP BY string;

Developer Notes:

1. This function is not case sensitive

2. Many functions that use NGrams8k will see a huge performance gain when the optimizer

creates a parallel query plan. One way to get a parallel query plan (if the optimizer

does not chose one) is to use make_parallel by Adam Machanic which can be found here:

sqlblog.com/blogs/adam_machanic/archive/2013/07/11/next-level-parallel-plan-porcing.aspx

3. When @N is less than 1 or greater than the datalength of the input string then no

tokens (rows) are returned.

4. This function can also be used as a tally table with the position column being your

"N" row. To do so use REPLICATE to create an imaginary string, then use NGrams8k to

split it into unigrams then only return the position column. NGrams8k will get you up

to 8000 numbers. There will be no performance penalty for sorting by position in

ascending order but there is for sorting in descending order. To get the numbers in

descending order without forcing a sort in the query plan use the following formula:

N = <highest number>-position+1.

Pseudo Tally Table Examples:

--===== (1) Get the numbers 1 to 100 in ascending order:

SELECT N = position FROM dbo.NGrams8k(REPLICATE(0,100),1);

--===== (2) Get the numbers 1 to 100 in descending order:

DECLARE @maxN int = 100;

SELECT N = @maxN-position+1

FROM dbo.NGrams8k(REPLICATE(0,@maxN),1)

ORDER BY position;

-- note: you don't need a variable, I used one to make the example easier to understand.

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

Revision History:

Rev 00 - 20140310 - Initial Development - Alan Burstein

Rev 01 - 20150522 - Removed DQS N-Grams functionality, improved iTally logic. Also Added

conversion to bigint in the TOP logic to remove implicit conversion

to bigint - Alan Burstein

Rev 03 - 20150909 - Added logic to only return values if @N is greater than 0 and less

than the length of @string. Updated comment section. - Alan Burstein

Rev 04 - 20151029 - Added ISNULL logic to the TOP clause for the @string and @N

parameters to prevent a NULL string or NULL @N from causing "an

improper value" being passed to the TOP clause. - Alan Burstein

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

RETURNS TABLE WITH SCHEMABINDING AS RETURN

WITH

L1(N) AS

(

SELECT 1

FROM (VALUES -- 90 NULL values used to create the CTE Tally table

(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),

(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL),(NULL)

) t(N)

),

iTally(N) AS -- my cte Tally table

(

SELECT TOP(ABS(CONVERT(BIGINT,(DATALENGTH(ISNULL(@string,''))-(ISNULL(@N,1)-1)),0)))

ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) -- Order by a constant to avoid a sort

FROM L1 a CROSS JOIN L1 b -- cartesian product for 8100 rows (90^2)

)

SELECT

position = N, -- position of the token in the string(s)

token = SUBSTRING(@string,CAST(N AS int),@N) -- the @N-Sized token

FROM iTally

WHERE @N > 0 AND @N <= DATALENGTH(@string); -- force the function to ignore a "bad @N"

The solution:

DECLARE @string varchar(1000) = 'The quick brown fox jumps over the lazy dog',

@searchString varchar(100) = 'the';

SELECT COUNT(*)

FROM dbo.NGrams8k(@string,LEN(@searchString))

WHERE token = @searchString;

if you need case sensitivity you would change the last line to WHERE token = @searchString COLLATE Latin1_General_BIN;

"I cant stress enough the importance of switching from a sequential files mindset to set-based thinking. After you make the switch, you can spend your time tuning and optimizing your queries instead of maintaining lengthy, poor-performing code."

-- Itzik Ben-Gan 2001