1.使用ifnull()函数，失败

如：SELECT ifnull(max(t.order_num), 0) FROM biodata.taxon as t where t.status='1';

报错：Caused by: org.hibernate.QueryException: No data type for node: org.hibernate.hql.internal.ast.tree.MethodNode

2.使用coalesce()函数，成功

如：SELECT coalesce(max(t.order_num), 0) FROM biodata.taxon as t where t.status='1';