Select Most Recent Distinct Customer Row

Question

I have a table that stores customer sales date like this:

|CustomerId|SalesDate |Product|Price|
|1         |2015-01-01|A      | 5.00|
|1         |2015-02-01|A      |10.00|
|1         |2015-03-01|B      | 7.00|
|2         |2015-01-15|A      | 9.00|

I'd like to select a single row for each customer who has purchased product A. If a customer has purchased product A more than once, I'd like to only see the most recent purchase.

This is the desired output:

|CustomerId|SalesDate |Product|Price|
|1         |2015-02-01|A      |10.00|
|2         |2015-01-15|A      | 9.00|

I've tried different versions of a group by/having queries like this:

SELECT CustomerId, SalesDate, Product, Price
FROM Sales
WHERE Product = 'A'
GROUP BY CustomerId
HAVING MAX(SalesDate);

Answer 1

Just grab the max of sales date in the select statement.

select customerid, max(salesdate) as salesdate, 'A'
from sales
where product = 'A'
group by customerid

with new requirements

select customerid, maxsalesdate, Product, Price
from sales
join (select customerid, max(salesdate) as maxsalesdate
      from sales
      where product = 'A'
      group by customerid) as sub on 
        sub.customerid = sales.customerid and 
        sub.maxsalesdate = sales.salesdate
where product = 'A'

Answer 2

Do this using a join and aggregation:

select s.*
from sales s join
     (select customerid, max(salesdate) as salesdate
      from sales s
      where product = 'A'
      group by customerid
     ) cs
     on s.customerid = cs.customerid and s.salesdate = cs.salesdate
where s.product = 'A';

The aggregation gets the maximum sales date for each customer. The join selects the row that matches that information.