so I have three tables in a database on a Microsoft SQL Server.
The system is an example one for learning, and it contains table A, which is schools that have an id and a total amount of money spent on buying stuff.
Table B contains the stuff you can buy with an id and price
Table C contains all orders, and order_id, school_id, stuff_id, and amount of stuff
My problem is this, I have to create a trigger that when a value is inserted in table C updates all schools total amount of money spent. And I can't figure out how to do that. Especially since i have to count the amount of things bought aswell.
If you want to see the sql as I do you can do it here: http://sqlfiddle.com/#!6/265f0
You want a query that is like this:
select c.school_id, sum(b.price) from b join c on b.stuff_id = b.stuff_id group by c.school_id;
You can use triggers. But this gets much more complicated, because you have to handle deleted and updating records, as well as inserting them.