Re: aggregation in mysql

[luca ghionna]

Hi, thank you for your reply.

an example might be the following (just to give a rough idea):

given a relation order(id_ord, amount) and transaction (trans_id, ord_id) you want:

select id_ord,sum(amount) from order,transaction where id_ord=ord_id group-by id_ord

you can easily perform a group on ord_id and count for each of them the number of transactions involved and then join the result with order to have the correct sum (you can write this by a simple rewritten sql query).

Is there any technical report available to test optimization policy of mysql?