Question

Suppose I have a table like this:

id | dates | customer | sale

And want to select, for each customer:

• number of purchases
• last purchase value
• total amount of purchases, when it has a positive value

With this table definition:

CREATE TABLE sales (
    id int auto_increment primary key, 
    dates date,
    customer int,
    sale int
);

And this data:

INSERT INTO sales
    (dates, customer, sale)
VALUES
    ('2012-01-01', 1, 2),
    ('2012-02-01', 1, 8),
    ('2012-03-01', 2, 1),
    ('2012-04-01', 2, 7),
    ('2012-05-01', 2, -5),
    ('2012-06-01', 1, 5)

My results should be:

customer | sales | last_sale
1           3        5
2           3        7

I cannot figure out how to get it. I have reached this:

SELECT s.customer, COUNT(s.sale) total_sales, last_sale FROM sales AS s
JOIN
  (SELECT customer, sale last_sale FROM sales GROUP BY customer ORDER BY dates DESC) AS t
  ON t.customer=s.customer
GROUP BY s.customer

But it is not working. Any ideas of how to get this data?

All code is in SQL fiddle

Answer 1

Try this

SELECT a.customer, count(a.sale), max_sale
FROM sales a
INNER JOIN (SELECT customer, sale max_sale 
            from sales x where dates = (select max(dates) 
                                        from sales y 
                                        where x.customer = y.customer
                                        and y.sale > 0
                                       )

           )b
ON a.customer = b.customer
GROUP BY a.customer, max_sale;

SQL DEMO