Using Linq to select the first and last values

I want to get just the first and last values in a date range. I have the following code:

using (var myEntities = new dataEntities())
  {
      var myValues = (from values in myEntities.PointValues
                      where values.PointID == dataValue && values.DataTime >= fromDate && values.DataTime  { myValues.First(), myValues.Last() };
      return myBarChart;
  }

This seems inefficient to me as I select the entire date range values initially. I can't seem to find a way to put first and last into the select command. Surely there must be a way to do this?

In response to Svick.

So, if I do this:

var firstValue = (from values in myEntities.PointValues
                      where values.PointID == dataValue && values.DataTime >= fromDate && values.DataTime = fromDate && values.DataTime <= toDate
                        orderby values.DataTime
                        select new BarChartValue
                        {
                            Time = values.DataTime,
                            Value = values.DataValue
                        }).Last();

Is that the best way to do it? I don't have any profiling tools (or if I do, I'm unsure how to use them).

The solution as provided by svick is:

var myValues = (from values in myEntities.PointValues
                      where values.PointID == dataValue && values.DataTime >= fromDate && values.DataTime  { myValues.First(), myValues.OrderByDescending(p => p.Time).First() };

A lot of this comes from my lack of understanding of the difference between IQueryable, IEnumerable and List. Here is a good explanation that helped me understand a bit more of what's going on:

https://stackoverflow.com/questions/4844660/differences-between-iqueryable-list-ienumerator

What you could do is to remove the ToList() from your query. This would change your code from making a single query that returns many values to two queries, each returning a single value.

StackExchange Code Review Q#25769, answer score: 4