Question

I have a left outer join (below) returning results as expected. I need to limit the results from the ‘right’ table to the ‘first’ hit. Can I do that somehow? Currently, I get a result for every record in both tables, I only want to see one result from the table on the left (items) no matter how many results I have in the right table (photos).

        var query = from i in db.items                 join p in db.photos                 on i.id equals p.item_id into tempPhoto                 from tp in tempPhoto.DefaultIfEmpty()                 orderby i.date descending                  select new                 {                     itemName = i.name,                     itemID = i.id,                     id = i.id,                     photoID = tp.PhotoID.ToString()                 };       GridView1.DataSource = query;     GridView1.DataBind(); 

Answer 1

This will do the job for you.

from i in db.items let p = db.photos.Where(p2 => i.id == p2.item_id).FirstOrDefault() orderby i.date descending select new {   itemName = i.name,   itemID = i.id,   id = i.id,   photoID = p == null ? null : p.PhotoID.ToString(); } 

I got this sql when I generated it against my own model (and without the name and second id columns in the projection).

SELECT [t0].[Id] AS [Id], CONVERT(NVarChar,(     SELECT [t2].[PhotoId]     FROM (         SELECT TOP (1) [t1].[PhotoId]         FROM [dbo].[Photos] AS [t1]         WHERE [t1].[Item_Id] = ([t0].[Id])         ) AS [t2]     )) AS [PhotoId] FROM [dbo].[Items] AS [t0] ORDER BY [t0].[Id] DESC 

When I asked for the plan, it showed that the subquery is implemented by this join:

<RelOp LogicalOp='Left Outer Join' PhysicalOp='Nested Loops'>