怎么将全表中的 null值或空值，全部替换成 ‘NN’

如何将全表中的 null值或空值，全部替换成 ‘NN’
全表300多列，800多行。
其中40%为空值或null。

请教如何用语句把所有空值或null全部替换成NN.

谢谢

[解决办法]
确定把全部空值或NULL都替换成NN

SQL code

update tb set col='NN' where col='' or col is NULL
[解决办法]
SQL code
declare @colname  varchar(100),        @sql      varchar(3000)set @sql=''select  @colname=name from syscolumns where id=object_id('tb') set @sql='update tb set'+''+@colname+''+'=NN'+'where col='' or col is NULL'exec (@sql)
[解决办法]
SQL code
declare @colname  varchar(100),        @sql      varchar(8000)set @sql=''declare cur_tbcolumn cursorforselect  name from syscolumns where id=object_id('tb') fetch next from cur_tbcolumnwhile @@fetch_status=0beginset @sql='update tb set '+@colname+'=''NN'''+'where '+@colname+'='''' or '+@colname+' is NULL'exec (@sql)set @sql=''fetch next from cur_tbcolumnend
[解决办法]
SQL code
declare @colname  varchar(100),        @sql      varchar(8000)set @sql=''declare cur_tbcolumn cursorforselect  name from syscolumns where id=object_id('tb') OPEN cur_tbcolumnfetch next from cur_tbcolumnwhile @@fetch_status=0beginset @sql='update tb set '+@colname+'=''NN'''+'where '+@colname+'='''' or '+@colname+' is NULL'exec (@sql)set @sql=''fetch next from cur_tbcolumnend