Question

I have a table:

Group | BasalArea | SpeciesName
1     | 3.6       | Palustris
1     | 45.0      | MSO
2     | 4.2       | Oak
2     | 2.0       | MSO
...

From this table, I would like to get the species name with the highest basal area grouped by the Group field, which would look like this:

Group | BasalArea | SpeciesName
1     | 45.0      | MSO
2     | 4.2       | Oak

Using SQL, I can get the highest basal area:

SELECT Group, Max(BasalArea)
FROM TABLE
GROUP BY Group

I can’t figure out how to also get the species name without doing some looping. Is this possible? What are the strategies for handling ties?

Answer 1

This is simpler in LINQ2SQL than in SQL:

var res = source.MyTable
    .GroupBy(item => item.Group)
    .Select(g => g.OrderByDescending(item => item.BasalArea).First())
    .ToList();

This will return the list of items with largest values of BasalArea in its Group, together with SpeciesName.

In SQL you would need to join back to the original table, like this:

SELECT * FROM TABLE b
JOIN (
    SELECT Group, Max(BasalArea) as BasalArea
    FROM TABLE
    GROUP BY Group
) t on t.Group = b.Group AND t.BasalArea = b.BasalArea