初步断定在@a里没找到
  继续追踪原因

  原来如此,charindex都找不到它,得right一下才把这根刺挑出来。当是char(1)等等的时候是可以的,replace(@a,char(1) ,’a’)
  这样是成功的,char(0)对应空字元,不对应数据库的NULL哦。
  既然这样,那用截取字符串的方法把需要的信息拿出来,框架大概如下,套个循环。当然也有可能有更好的方法,仅供参考
loop
UPDATE  TblName  SET
ColName = LEFT(ColName,LEN(ColName)-1)
WHERE ASCII(RIGHT( ColName ,1))=0
end loop
  下面共享个通用处理指定表中所有列中所有不可见字符的处理脚本,实测可用。
SET NOCOUNT ON
DECLARE @TblName  VARCHAR(100)
DECLARE @UpdateString NVARCHAR(1000)
DECLARE @SelectString NVARCHAR(1000)
DECLARE @COlName VARCHAR(100)
DECLARE @COUNT  INT
SET @TblName = '表名称'--指定想要修改的表名
--定义游标取出指定表内的数据类型是VARCHAR,char,nVARCHAR的字段名称
DECLARE cur_ColName  CURSOR
FOR
SELECT col.name
FROM syscolumns AS col
inner join sysobjects  AS obj  ON col.ID = obj.ID
INNER join systypes  AS typ  ON col.xtype = typ.xtype
WHERE obj.xtype ='U'
AND obj.name = @TblName
AND typ.name IN ('VARCHAR','CHAR','NVARCHAR','NCHAR')
FOR READ ONLY
--打开游标
OPEN cur_ColName
FETCH NEXT FROM cur_ColName INTO @ColName
IF @@FETCH_STATUS0
BEGIN
PRINT '没有对应表或字段,'PRINT '请确认当前数据库内有' + @TblName + '表,' PRINT '或该表内有VARCHAR、CHAR、NVARCHAR、NCHAR类型的字段!' GOTO LABCLOSE
END--循环修改
WHILE @@FETCH_STATUS=0
BEGIN
--拼修改字符串
--去掉左边的不可见字符
SET @SelectString = 'SELECT @COU=COUNT(*)
FROM ' + @TblName +'
WHERE ASCII(LEFT(' + @ColName +',1))'+ @ColName + ' IS NOT NULL'
EXEC sp_executesql @SelectString,N'@COU INT OUTPUT',
@COUNT OUTPUT WHILE @COUNT>0
BEGIN
SET @UpdateString =
' UPDATE ' + @TblName +
' SET ' + @ColName + '=RIGHT(' + @ColName + ',LEN(' + @ColName + ')-1)
WHERE ASCII(LEFT(' + @ColName + ',1))' + @ColName + ' IS NOT NULL'
EXEC sp_executesql @UpdateString
EXEC sp_executesql @SelectString,N'@COU INT OUTPUT',@COUNT OUTPUT
END
--去掉右边的不可见字符
SET @SelectString = 'SELECT @COU=COUNT(*)
FROM ' + @TblName +'
WHERE ASCII(RIGHT(' + @ColName +',1))'+ @ColName + ' IS NOT NULL'
EXEC sp_executesql @SelectString,N'@COU INT OUTPUT',
@COUNT OUTPUT WHILE @COUNT>0
BEGIN
SET @UpdateString =   ' UPDATE ' + @TblName +   ' SET '
+ @ColName + '=LEFT(' + @ColName + ',LEN(' + @ColName + ')-1)
WHERE ASCII(RIGHT(' + @ColName + ',1))' + @ColName + ' IS NOT NULL'
EXEC SP_EXECUTESQL @UpdateString
EXEC sp_executesql @SelectString,N'@COU INT OUTPUT',
@COUNT OUTPUT
END
PRINT 'column: ' + @ColName + '---ok'
FETCH NEXT FROM cur_ColName INTO @ColName
END
--关闭、释放游标
LABCLOSE: CLOSE cur_ColName
DEALLOCATE cur_ColName
GO