Question

A sample linq query from MSDN:

var expensiveInStockProducts =
    from p in products
    where p.UnitsInStock > 0 && p.UnitPrice > 3.00M
    select p;

Does this query select EVERY column from the database table immediately, or does it return some sort of pointer that retieves the actual column data on demand? ie. If there are 50 columns in my table and I only use a single p.UnitsInStock in my actual code, then am I retrieving 50 times more data than I expected?

Answer 1

if you debugged that then you would probably see every column in your products table in the SELECT ... portion of the query

if you did select p.UnitsInStock you would only see that in the SELECT ... portion of the query.

So to answer your question, yes, it does select every column unless you specify what you want or dump the selection into an anonymous object like so:

var expensiveInStockProducts =
    from p in products
    where p.UnitsInStock > 0 && p.UnitPrice > 3.00M
    select new { p.UnitsInStock, p.SomeOtherColumn }