DBI 1.29 is out. There is a change in the specification. (And possibly a discrepancy in previous releases, read on.)
fetchrow_array in scalar context is not guaranteed to return the first column, as previously stated.

I am posting this warning because I have seen some SOPWs where people were using this particular idiom.

I quote from the release notes:
Changes in DBI 1.29, 15th July 2002

NOTE: This release changes the specified behaviour for the fetchrow_array method when called in a scalar context: The DBI spec used to say that it would return the FIRST field. Which field it returns (i.e., the first or the last) is now undefined. This does not affect statements that only select one column, which is usually the case when fetchrow_array is called in a scalar context.
FYI, this change was triggered by discovering that the fetchrow_array implementation in Driver.xst (used by most compiled drivers) didn't match the DBI specification. Rather than change the code to match, and risk breaking existing applications, I've changed the specification (that part was always of dubious value anyway).
Rather than using fetchrow_array in scalar context, consider calling it by assigning to a one-element list:
my $sth=$dbh->prepare("SELECT surname,name from people"); $sth->execute(); while (my ($surname) = $sth->fetchrow_array()) { # do something with $surname }
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.

One more warning, from the same source. Future versions of the DBI may not support Perl 5.5 any longer. If you have database applications, consider upgrading to Perl 5.6.1.
 _  _ _  _  
(_|| | |(_|><