Lookup with duplicate values - sql

Question

This is kind of a complicated question. I have three tables:
A PRODUCTS table
ProductID
ProductName
Product A
Edwardian Desk
Product B
Edwardian Lamp
And a GROUPS table
ProductGroup
ProductID
Group A
Product A
Group A
Product B
Group B
Product C
And a SALES table
Product ID
Sales
Product A
1000
Product B
500
And I need to show the total of Sales per Product Group.
This part I understand; I wrote the query:
SELECT Groups.ProductGroup, SUM(Sales) AS TotalSales
FROM Groups
JOIN Sales
ON Groups.ProductID=Sales.ProductID
GROUP BY Groups.ProductGroup
This is the part that confuses me though: for each group, I need to pull in one of the names of the products in the group. However, it does not matter which name is pulled. So the final data could show:
Group A, Edwardian Desk, 1500
or
Group A, Edwardian Lamp, 1500
How can I pull the name of the product into my query?
I am working in Microsoft SQL Server

Answer 1

There's a number of ways to bring in one of your product's names, a couple of options are to either use an aggregation with a correlated subquery or to to use an apply.
Note, I've used aliases for your table names - doing so is good practice and makes queries more compact and easier to read. Also - presumably this is a contrived example and not your actual tables - but generally it's not a good practice to have column names identical to the table name, so if Sales on table Sales represents a quantity, then just call it Quantity!
select g.ProductGroup,
(select Min(ProductName) from Products p where p.ProductId=g.ProductId) FirstProductAlphabetically,
Sum(s.Sales) as TotalSales
from Groups g
join Sales s on s.ProductID=g.ProductID
group by g.ProductGroup
select g.ProductGroup,
p.ProductName as FirstProductById,
Sum(s.Sales) as TotalSales
from Groups g
join Sales s on s.ProductID=g.ProductID
cross apply (
select top (1) p.ProductName
from Products p
where p.ProductId=g.ProductId
order by ProductId
)p
group by g.ProductGroup

Answer 2

You can add products to the JOIN and use an aggregation function:
SELECT g.ProductGroup, SUM(s.Sales) AS TotalSales,
MIN(p.ProductName)
FROM Groups g JOIN
Sales s
ON g.ProductID = s.ProductID JOIN
Products p
ON p.ProductID = s.ProductId
GROUP BY g.ProductGroup;
Note: I often add two columns, MIN() and MAX() to get two sample names.
I should add. Your sample data has ProductIds that are not in the Products. That suggests a problem with either the question (more likely) or the data model. If you actually have references to non-existent products, then use a LEFT JOIN to Products rather than an inner join.