CREATE FUNCTION D_ByteExchangeS_Byte(
@str NVARCHAR(4000), --要转换的字符串
@flag bit              --转换标志,0转换成半角,1转换成全角
)RETURNS nvarchar(4000)
AS
BEGIN
    DECLARE @pat nvarchar(8),@step int,@i int,@spc int
    IF @flag=0
        SELECT @pat=N‘%[！-～]%‘,@step=-65248,
            @str=REPLACE(@str,N‘　‘,N‘ ‘)
    ELSE
        SELECT @pat=N‘%[!-~]%‘,@step=65248,
            @str=REPLACE(@str,N‘ ‘,N‘　‘)
    SET @i=PATINDEX(@pat COLLATE LATIN1_GENERAL_BIN,@str)
    WHILE @i>0
        SELECT @str=REPLACE(@str,
                SUBSTRING(@str,@i,1),
                NCHAR(UNICODE(SUBSTRING(@str,@i,1))+@step))
            ,@i=PATINDEX(@pat COLLATE LATIN1_GENERAL_BIN,@str)
    RETURN(@str)
END
GO

调用 ：SELECT dbo.D_ByteExchangeS_Byte(N‘１９８９455‘,0) 

引用：http://blog.csdn.net/xiemk2005/article/details/6551873

sql server 2005全角与半角字符转换