1:sp_msforeachtable 用来loop表中的所有列
  2:更新类型为ntext,text类型的列时，先判断DATALENGTH(Column)是否大于8000字节，如果小于8000字节的话，我们可以使用
   update Table set Column=Replace(Cast(Column as varchar(8000)),'oldkeyword','newkeyword')来更新。
  
  源码如下：
  UpdateTextColumn
  Create proc [dbo].[UpdateTextColumn]
  @Table varchar(100),
  @Columns varchar(200),--eg:Column1,Column2,
  @old varchar(100),
  @new varchar(100)
  as
   set nocount on
   declare @sql nvarchar(2000)
   declare @Column varchar(50)
   declare @cpos int,@npos int
   set @cpos=1;
   set @npos=1;
   set @npos=charindex(',',@Columns,@cpos);
  
   while(@npos>0)
   begin
   set @Column = substring(@Columns,@cpos,@npos-@cpos);
   set @cpos = @npos+1
   set @npos=charindex(',',@Columns,@cpos);
  
   set @sql = 'update '+@Table+' set '+@Column+'=replace(cast('+@Column+' as varchar(8000)),@old,@new) where Datalength('+@Column+')<=8000';
   EXECUTE sp_executesql @Sql,
   N'@old varchar(100),@new varchar(100)',
   @old,
   @new
   declare @ptr binary(16) ,@offset int,@dellen int
  
   set @dellen = len(@old)
  
   set @offset = 1
   while @offset>=1
   begin
   set @offset = 0
   set @sql = 'select top 1 @offset = charindex('''+@old+''' , '+@Column+'), @ptr = textptr('+@Column+') from '+@Table+' where Datalength('+@Column+')>8000 and '+@Column+' like ''%'+@old+'%''';
   EXEC sp_executesql @Sql,N'@offset int OUTPUT,@ptr binary(16) OUTPUT,@old varchar(100)',
   @offset OUTPUT,@ptr OUTPUT,@old;
  
   if @offset > 0
   begin
   set @offset = @offset-1
  
   set @sql='updatetext '+@Table+'.'+@Column+' @ptr @offset @dellen @new';
   EXEC sp_executesql @Sql,N'@offset int ,@ptr binary(16),@dellen int,@new varchar(100)',@offset,@ptr,@dellen,@new;
   end
   end
  end
  go
  ReplaceKeyWord
  Create proc [dbo].[ReplaceKeyWord]
  @old nvarchar(100),
  @new nvarchar(100)
  as
  declare @sql nvarchar(1000)
  set @sql=N'
  declare @s nvarchar(4000),@tbname sysname
  select @s=N'''',@tbname=N''?''
  select @s=@s+N'',''+quotename(a.name)+N''=replace(''+quotename(a.name)+N'',N'''''+@old+''''',N'''''+@new+''''')''
  from syscolumns a,systypes b
  where a.id=object_id(@tbname)
  and a.xusertype=b.xusertype
  and b.name like N''%char''
  if @@rowcount>0
  begin
  set @s=stuff(@s,1,1,N'''')
  exec(N''update ''+@tbname+'' set ''+@s)
  end '
  --print @sql
  exec sp_msforeachtable @sql;
  
  set @sql=N'
  declare @s nvarchar(4000),@tbname sysname
  select @s=N'''',@tbname=N''?''
  select @s=@s+quotename(a.name)+N'',''
  from syscolumns a,systypes b
  where a.id=object_id(@tbname)
  and a.xusertype=b.xusertype
  and b.name like N''%text''
   if @@rowcount>0
  begin
  exec UpdateTextColumn @tbname,@s,'''+@old+''','''+@new+'''
  end
  ' ;
  exec sp_msforeachtable @sql
  go
  使用方法如下：Exec ReplaceKeyWord  '原来代码','新的代码'