FSO Database Error

The database has encountered a problem.

Error messages:

[Type] dbquery_error [1054] Unknown column 'pp.read_num' in 'order clause' [Query] SELECT pp.id,pp.mid,trim(pp.title) as title,pp.imgicon,pp.tags,from_unixtime(pp.create_time, '%Y%m%d') as filefolder,from_unixtime(pp.create_time, '%Y-%m-%d') as create_time,pp.readnum,pp.content FROM articles pp WHERE pp.status=1 order by pp.read_num desc LIMIT 0,16

Program messages:

[Line: 0020]/home/bestfreenow_iq/bestfreenow.com/article.php(ArticleModule::index) [Line: 0077]/home/bestfreenow_iq/bestfreenow.com/core/module/article.module.php(FDB::query)