Question

Let’s say I have a table that looks like this:

Id     CheckboxId     Selected     DateCreated
1      1              1            1/1/2010
2      2              1            1/2/2010
3      1              0            1/3/2010
4      3              1            1/4/2010
5      3              0            1/5/2010

CheckboxId is a FK and the table is just a history of when the boxes are checked or unchecked.

What I want to get is the most recent record for each CheckboxId. In the case of my demo table I want rows 2, 3, and 5. How would you accomplish this? Also I’m sure this is as easy as a “where” at the beginning of the query but if it could also be modified to only get records before a specified date that would be fantastic.

I’m having trouble figuring out how I would write a query to do this in SQL and it’s making a link query impossible. I’m sure it has to be a selection from a sub query of distinct checkboxIds coupled with a group by or something but my SQL just isn’t that great.

Many thanks for your help.

Answer 1

Should be something like this:

var results = (from x in context
       group x by x.CheckboxID into g
       select new
       {
           CheckboxID = g.Key,
           MaxItem = g.OrderByDescending(o => o.DateCreated).FirstOrDefault()
       });

Then you can do:

foreach (var x in results)
    x.MaxItem.Selected //...etc.