However, selecting two or more columns and then fetching only one is a plain waste of resources. If you need to fetch only the first column of a query, I recommend that you be specific and ask for that column only.
In some databases (I'm thinking of Informix in particular), fields in the ORDER BY clause must be in the SELECT clause, so maybe you want to select the customer with the highest balance, but don't really need the
balance itself, so you fetch the first field of the first row of this:
select customer, balance
order by balance desc