Hi!
There are some useful SQL structures, which are not so commonly used. For example I like the following syntax:
select * from vending_price where (product_id,valid_from) = (0,'2010-01-09');
It is basically the same than the following, but more compact and easier to read.
select * from vending_price where product_id = 0 and valid_from = '2010-01-09';