Select only fields using SOQL

Question

Is it possible to select only fields using SOQL? I mean to select fields without selecting whole SObjects?

For example, is it possible to select a List<Name> of names of accounts, such that accounts have Rating = 'Warm'?

I know about

List<Account> = [
    SELECT Name
    FROM Account
    WHERE Rating = 'Warm`
];

But I would like my list to have only names.

Answer 1

Not directly. You need to write your own loop e.g.:

List<String> names = new List<String>();
for (Account a : [
        select Name
        from Account
        where Rating = ‘Warm’
        order by Name
        ) {
    names.add(a.Name);
}

Answer 2

In the general sense, no, you cannot do this. The single exception to this by way of ID types using AggregateResult:

Set<Id> accountIds = new Map<Id, AggregateResult>([
  SELECT AccountId Id
  FROM Opportunity
  GROUP BY AccountId]).keySet();

This works by aliasing the lookup field to the special value Id (case sensitive), which we briefly turn in to a map, and get the key set for that map.

Obviously, this will not work for any other type of field, in which case you'll have to use a for loop, as mentioned by Keith's answer.