Is there a reason you are using Sybase::DBlib instead of the more usual DBI?

DBI has a handy selectcol_arrayref() function which folds a single-column resultset into an array reference.

sub sa_details {
  my $dbh = ...

  return $dbh->selectcol_arrayref(
    qq{SELECT userid FROM user}
  );
}

my $arrayref = sa_details();
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(Usually you use DBI with the prepare-execute-fetch combination, though. The select{row,all,col} functions are there just for convenience.)