创建别名函数失败

create alias function fn_get_isdate2(varchar) with PARAMETER(pstr) As
if (DATE_FORMAT(SUBSTR(replace(replace(replace(pstr,'-',''),'/',''),'.',''),1,8),'yyyy-MM-dd')is not null,"true","false");

doris版本：2.0.5， 请问这个是一个bug还是不支持这种写法了