發現在SQL Server中的字符串中的字符的出現次數

Question

假設字符串爲「這是字符串」

我必須定義一個表值函數輸出結果：

+------+-------+ 
| char | count | 
+------+-------+ 
|  | 3 | 
| t | 2 | 
| h | 1 | 
| i | 3 | 
| s | 3 | 
| a | 1 | 
| r | 1 | 
| n | 1 | 
| g | 1 | 
+------+-------+ 

應該如何我這樣做？

Answer 1

CREATE FUNCTION CountCharacterOccurences(@str nvarchar(max)) 
RETURNS TABLE 
AS 
RETURN 
    WITH Nums(n) -- Generate numbers from 1 to LEN(@str) 
    AS(
     SELECT 1 
     UNION ALL 
     SELECT n+1 
     FROM Nums 
     WHERE n+1 <= LEN(@str) 
    ) 
    SELECT 
     SUBSTRING(@str, n, 1) AS char, 
     COUNT(*) AS count 
    FROM Nums 
    GROUP BY SUBSTRING(@str, n, 1) 

使用

DECLARE @str VARCHAR(max) 
SET @str = 'this is a string'; 

SELECT * FROM CountCharacterOccurences(@str) 

返回

char count 
    3 
a 1 
g 1 
h 1 
i 3 
n 1 
r 1 
s 3 
t 2 

Answer 2

CREATE FUNCTION [dbo].[udfCharCount] (@String varchar(max)) 

Returns Table 

As 
Return 

    Select Char,Count=count(*) 
    From (
      Select Char = Substring(a.b, v.number+1, 1) 
      From (select @String b) a 
      Join master..spt_values v on v.number < len(a.b) where v.type = 'P' 
     ) A 
    Group By Char 


-- Syntax Select * from [dbo].[udfCharCount]('this is a string') 

返回

Char Count 
     3 
a  1 
g  1 
h  1 
i  3 
n  1 
r  1 
s  3 
t  2