Mysql query error  :  | SQL : select * from `blogread_article` 
			 where `idCate` = '21' 
			order by `id` desc 
			limit 20, 20<br />
<b>Fatal error</b>:  Uncaught Error: Call to a member function fetch_assoc() on null in /data1/www/htdocs/511/blogread/1/includes/base/db.mysqli.class.php:61
Stack trace:
#0 /data1/www/htdocs/511/blogread/1/includes/base/db.mysqli.class.php(50): yayuMySQLi-&gt;fetch_assoc('select * from `...')
#1 /data1/www/htdocs/511/blogread/1/it/includes/db/dbArticle.class.php(48): yayuMySQLi-&gt;assoc_arr('select * from `...')
#2 /data1/www/htdocs/511/blogread/1/it/category.php(98): db_article-&gt;article_list_get(20, 20, '21')
#3 {main}
  thrown in <b>/data1/www/htdocs/511/blogread/1/includes/base/db.mysqli.class.php</b> on line <b>61</b><br />