Mendix support subquery in select clause and from Clause, subquery return only one column it will not return multiple columns
Syntax as below
select c.Name, count(o.TotalPrice) c,
(select FirstName from "Sales.Customer" d where d.Name = c.Name) w
from "Sales.Customer" c
left join "c/Sales.Order_Customer/Sales.Order" o
group by c.Name
having count(o.TotalPrice) > 1
You can check above query in this portal:
https://mydemoversion8-sandbox.mxapps.io/p/OQL