Question

Is this:

Dim mydata = (From c In dc.Table Select New With {c.ID}).Count

any faster than this:

Dim mydata = (From c In dc.Table Select c).Count

assuming the table has a good number of fields?

Answer 1

The short answer: no.

The SQL generated by the LINQ-to-SQL engine should be essentially the same for both forms (if not exactly the same) because you’re calling .Count() immediately on the query.

A compiled query version, on the other hand, would be faster after the first execution. Here’s one way to do a compiled query for this:

Public Shared FetchCount As Func(Of DataContext, Integer) = _
    CompiledQuery.Compile(Function(context as DataContext) _
        (From c in context.Table Select c).Count())

DataContext would need to be the Type of the LINQ-to-SQL DBML, and Table would need to be the appropriate table. And, I believe you’ll need to import System.Data.Linq to have access to CompiledQuery.