OData uri conventions documentation. Our API closely adheres to these conventions with a few additional extensions.
Grouping
$groupby=Key,Select
$groupby=new(SalesOrderNum),new(Price,Quantity)&$select=Key/SalesOrderNum,Sum(Price mul Quantity) as Total
Contains
$filter=contains( new[2,3,5,9], SalesOrderNum) will give you sales orders in the list 2,3,5,9