功能沒有回到我所期望的

Question

這隻返回NULL。它應該剝離特殊的章程。任何想法，爲什麼它不工作？

感謝您的幫助。

Create Function [dbo].[RemoveNonAlphaCharacters] 
    (@Temp VarChar(2000)) 
Returns VarChar(2000) 
AS 
Begin 
    Declare @ReturnVal as VarChar(2000) 
    Declare @TopChar as int 
    Declare @BottomChar as int 
    Declare @Index as Int 

    Set @Index = 0 
    Set @TopChar = ASCII(' ') 
    Set @BottomChar = ASCII('~') 

    While @Index < LEN(@Temp) 
    Begin 
     Set @Index = @Index + 1 
     if (ASCII(SUBSTRING(@Temp, @Index, 1)) >= @TopChar AND ASCII(SUBSTRING(@Temp, @Index, 1)) <= @BottomChar) 
      Select @ReturnVal = @ReturnVal + SUBSTRING(@Temp, @Index, 1); 
    End 

    Return @ReturnVal; 
End 

Answer 1

你需要初始值作爲

Declare @ReturnVal as VarChar(2000) = '' 

因爲空+什麼= NULL

或者你可以使用ISNULL()功能類似下面的

Select @ReturnVal = ISNULL(@ReturnVal,'') + SUBSTRING(@Temp, @Index, 1); 

Answer 2

對於討厭快速設置爲基礎的解決方案，將執行更好，您可以使用此：

IF OBJECT_ID('dbo.AlphaOnly') IS NOT NULL DROP FUNCTION dbo.AlphaOnly; 
GO 
CREATE FUNCTION dbo.AlphaOnly (@pString varchar(8000)) 
RETURNS TABLE WITH SCHEMABINDING AS RETURN 
/**************************************************************************************** 
Purpose: 
Given a VARCHAR(8000) or less string, returns only the alphabetical digits from the 
input string (@pString). 

Compatibility: 
SQL Server 2008+, Azure SQL Database, Azure SQL Data Warehouse & Parallel Data Warehouse 

Parameters: 
@pString = varchar(8000); Input string to be cleaned 

Returns: 
AlphaOnly - nvarchar(max) 

Syntax: 
--===== Autonomous 
SELECT ca.AlphaOnly 
FROM dbo.AlphaOnly(@pString) ca; 

--===== CROSS APPLY example 
SELECT ca.AlphaOnly 
FROM dbo.SomeTable st 
CROSS APPLY dbo.AlphaOnly(st.SomeVarcharCol) ca; 

Programmer's Notes: 
1. Based on Jeff Moden/Eirikur Eiriksson's DigitsOnlyEE function. For more details see: 
    http://www.sqlservercentral.com/Forums/Topic1585850-391-2.aspx#bm1629360 

2. This is an iTVF (Inline Table Valued Function) that performs the same task as a 
    scalar user defined function (UDF) accept that it requires the APPLY table operator. 
    Note the usage examples below and see this article for more details: 
    http://www.sqlservercentral.com/articles/T-SQL/91724/ 

    The function will be slightly more complicated to use than a scalar UDF but will yeild 
    much better performance. For example - unlike a scalar UDF, this function does not 
    restrict the query optimizer's ability generate a parallel query plan. Initial testing 
    showed that the function generally gets a 

3. AlphaOnly runs 2-4 times faster when using make_parallel() (provided that you 
    have two or more logical CPU's and MAXDOP is not set to 1 on your SQL Instance). 

4. CHECKSUM returns an INT and will return the exact number given if given an INT to 
    begin with. It's also faster than a CAST or CONVERT and is used as a performance 
    enhancer by changing the BIGINT of ROW_NUMBER() to a more appropriately sized INT. 

5. Another performance enhancement is using a WHERE clause calculation to prevent 
    the relatively expensive XML PATH concatentation of empty strings normally 
    determined by a CASE statement in the XML "loop". 

6. Note that AlphaOnly returns an nvarchar(max) value. If you are returning small 
    numbers consider casting or converting yout values to a numeric data type if you are 
    inserting the return value into a new table or using it for joins or comparison 
    purposes. 

8. AlphaOnly is deterministic; for more about deterministic and nondeterministic 
    functions see https://msdn.microsoft.com/en-us/library/ms178091.aspx 

Usage Examples: 
--===== 1. Basic use against a literal 

SELECT ao.AlphaOnly 
FROM dbo.AlphaOnly('xxx123abc999!!!') ao; 

--===== 2. Against a table 
DECLARE @sampleTxt TABLE (txtID int identity, txt varchar(100)); 
INSERT @sampleTxt(txt) VALUES ('!!!A555A!!!'),(NULL),('AAA.999'); 

SELECT txtID, OldTxt = txt, AlphaOnly 
FROM @sampleTxt st 
CROSS APPLY dbo.AlphaOnly(st.txt); 

--------------------------------------------------------------------------------------- 
Revision History: 
Rev 00 - 20170411 - Inital Creation - Alan Burstein 
****************************************************************************************/ 
WITH 
E1(N) AS (SELECT N FROM (VALUES ($),($),($),($),($),($),($),($),($),($)) x(n)), 
iTally(N) AS 
( 
    SELECT TOP (LEN(ISNULL(@pString,CHAR(32)))) 
    (CHECKSUM(ROW_NUMBER() OVER (ORDER BY (SELECT NULL)))) 
    FROM E1 a CROSS JOIN E1 b CROSS JOIN E1 c CROSS JOIN E1 d 
) 
SELECT AlphaOnly = 
( 
    SELECT SUBSTRING(@pString,N,1) 
    FROM iTally 
    WHERE ((ASCII(SUBSTRING(@pString,N,1)) - 65) & 0x7FFF) < 26 
    OR ((ASCII(SUBSTRING(@pString,N,1)) - 97) & 0x7FFF) < 26 
    FOR XML PATH('') 
); 

用於該功能的邏輯基於其可以在這裏找到我的DigitsOnlyEE及AlphaNumericOnly功能：DigitsOnlyEE and AlphaNumericOnly