Question

Why this linq query:

(from c in Orders
select new 
{
   Id=c.Id, 
   DeliveryDate = c.DeliveryDate.Value
}).Take(10)

is translated into

SELECT TOP (10) [t1].[Id], [t1].[value] AS [DeliveryDate]
FROM (
    SELECT [t0].[Id], [t0].[DeliveryDate] AS [value]
    FROM [Orders] AS [t0]
    ) AS [t1]

but when I change DeliveryDate = c.DeliveryDate.Value into DeliveryDate = c.DeliveryDate SQL query looks as simple as:

SELECT TOP (10) [t0].[Id], [t0].[DeliveryDate]
FROM [Orders] AS [t0]

Answer 1

I think this is because the LINQ2SQL‘s translator is under-optimized. Use of a “property” (Value) triggers creation of a sub-query, which turns out to be unnecessary.

It is worth to note that any RDBMS worth its salt would generate identical query plans for both SQL queries, so in the end it would not matter either way.