I agree with Jeffa absolutely 100%. I have one caveat though:

I like use "?" to indicate where I'll be filling in data. I do this so that I can have one generic subroutine that I can call from almost anywhere. Here is such a subroutine that I can pull off the top of my head:

# assume strict, and all other typical good code practices
my $column    = "UserName";
my $condition = "UserID";
my $qualifier = "101";

my ($rowcount, $UserID) = SQL_select($column, $condition, $qualifier);

sub SQL_select {
  my $col  = shift;
  my $cond = shift;
  my $qual = shift;

  my $sth = $dbh->("SELECT ? FROM DB.Table WHERE ? = ?");
  $sth->execute($col, $cond, $qual);

  my $rowcount = $sth->rows;
  my $UserID   = $sth->fetchrow_hashref;

  return ($rowcount, $UserID);
}
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Now, all you have to do is make sure you define the column, condition and qualifiers as needed. Of course, you'd probably want to get more complicated than this. You'd probably want some error checking and what-not (I'm on lunch...didn't get to stick it in there).

As a side note, notice I counted the rows. I've always done that, and I think it's a good idea (even if you're using a LIMIT function in the Database query) as a form of error checking. Obviously, this is a generic subroutine...so who knows what the guy is looking for. Supposing he is doing a query to find a UserName for someone with a UserID of 101 (as in this case). Well, if there are no rows returned, you'll probably want to report that the user doesn't exist. Or, if more than one is returned, you'll want to maybe take some other measures to notify the system maintainer that there is more than one UserName registered to that UserID. A whole set of other subroutines might be called if this is the case. So, it's always good to count rows.

--Coplan