Linq, is select().SingleorDefault() a bad idea?

 var queueitem = context.CrawlerQueues.
                 Select(cq => new{cq.Guid,cq.Result}).
                 SingleOrDefault(cq => cq.Guid == guid);

Is above a bad idea, will it first select all database rows and then find the one or will it be smart and see the context its used within and only fetch the one row.

Reason for doing this is i want to return only the Guid and the Result coloums.

return Newtonsoft.Json.JsonConvert.SerializeObject(queueitem, Formatting.Indented);

How would i find the answer to this without having to monitor network flow or the requests made to the database?