$art = M("ArticleClass");
$artlist = $art->order("RootID,OrderID")->select();
sql语句为：
SELECT T1.* FROM (SELECT ROW_NUMBER()
OVER ( ORDER BY RootID,OrderID) AS ROW_NUMBER,
thinkphp.* FROM
(SELECT ClassName,ClassID,RootID,OrderID FROM article_class)
AS thinkphp) AS T1 WHERE (T1.ROW_NUMBER BETWEEN 1 AND 1)

建议 T1.ROW_NUMBER BETWEEN 1 AND 1 在selelct的时候修改成1=1比较好