create table orders (
    id integer primary key,
    product text,
    timestamp time
);

>>> from blaze import data, by, compute
>>> url = "postgresql:///testdb"
>>> db= data(url)
>>> orders = db['orders']

pairs = by(orders['product'], max_timestamp=orders['timestamp'].max())

# computing the above produces the following sql
SELECT orders.product, max(orders.timestamp) as max_timestamp
FROM orders
GROUP BY orders.dataset limit 10001

expression = orders[(orders['product'] == pairs['product']) & (orders['timestamp'] == pairs['max_timestamp'])]

# computing the above produces the following sql
SELECT orders.id, orders.product, orders.timestamp FROM orders
WHERE orders.product =  orders.product
AND  orders.timestamp = max(orders.timestamp) limit 10001