How 'expensive' are DB queries? for example

my opening page has a function that counts all ‘eye doctors’ in each
town ( there are about 20 towns) and displays that number next to the
town name in the view. therefore that is about 20 queries on the given

i was just wondering how expensive is this operation and should i be
finding an alternative?
especially if that town number is increased to lets say 40-60?


if you use eager loading (with :has_many associations) you can reduce
20 or so queries to 1.

Heri R.