Question

这只会返回NULL。它应该剥离特别的章程。任何想法为什么它不起作用？

感谢您的帮助。

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

您需要将值初始化为

 Declare @ReturnVal as VarChar(2000) = ''

因为null + anything = null

或者您可以使用ISNULL()功能，如下所示

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

Answer 2

对于一个令人讨厌的基于快速集的解决方案，它可以更好地运行：

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('') 
);

此函数使用的逻辑基于我的DigitsOnlyEE和AlphaNumericOnly函数，可在此处找到：DigitsOnlyEE and AlphaNumericOnly

功能不能恢复我的期望

2 个答案: