Question

Is it possible in LINQ to do this: Group by a field (LineTotal), returning only the top 9 groups and then in the 10th group return the sum of all other groups?

In SQL server this can be done like so:

with TopGroups as 
(
    select sum(sol.LineTotal) as ProductGroupSales, p.ProductGroupId,
    ROW_NUMBER() OVER(ORDER BY sum(sol.LineTotal) DESC) as Num
    from SalesOrderLines sol left join Products p on p.Id = sol.ProductId
    group by p.ProductGroupId
)
select ProductGroupSales from TopGroups where Num < 10
union all
select sum(ProductGroupSales) from TopGroups where Num >= 10

Can this be translated to LINQ? I’m not sure how ROW_NUMBER() OVER() and union all translate to LINQ.

Answer 1

1. You can translate the row number using “.Take(9)” and “.Skip(0).Take(1)“.
2. UNION ALL maps to seqA.Concat(seqB)
3. A CTE maps to just a variable holding a query. Like so:

–

var q1 = SalesOrderLines.Where(...);
var q2 = q1.Concat(q1); //reused q1 multiple times for q2 like a CTE

All of these basically come at no performance cost on the SQL side.