Triggers aren't granular. When using the before update trigger, you can use variables like the Trigger.New
and Trigger.OldMap
in order to correlate each record to see if the fields you're interested in have changed.
for (Opportunity newOpp : Trigger.new) {
Opportunity oldOpp = Trigger.oldMap.get(newOpp.Id);
if (oldOpp.Name != newOpp.Name) {
// do something
}
}