Here's an example script that I loosely based on your script.

#!/usr/bin/perl
use strict;
use warnings;
use DBI;

my $dbh = DBI->connect("DBI:mysql:database=test;user=auser;password=ap
+wd",
    {RaiseError => 1, PrintError => 1});

# set up error handling
$dbh->{HandleError} = sub { handle_error(@_) };

my $sql = 'select wrong_col, correct_col from test limit 10';

our $handle_it; # This is only needed for this contrived example

for $handle_it ( 0 .. 1 ) {
  print "\n", "-" x 40, "\n\n" if $handle_it;
  print "Trying HandleError (with RaiseError on):\n";
  print "handle it?  ", ($handle_it) ? 'yes' : 'no', "\n";

  my $hashref = $dbh->selectall_hashref($sql, 'filename'); 

  print "$_\t-->\t$hashref->{$_}\n" for (keys %{$hashref});
  print "errstr says: ", $dbh->errstr, "\n" if $dbh->errstr;
}

sub handle_error {
  my ($error, $dbh) = @_;
  my $handled = 0; # did we handle the error?

  print "\n\tSub 'handle_error': $error\n";

  if ( $handle_it ) {    # if you want to say this error is not an err
+or
    # clear the error
    $dbh->set_err(undef,undef);

    # set the new return value
    $_[2] = { wrong_col => 'bar', correct_col => 'foo' };

    # update our handled flag
    $handled = 1;

  } else {      # we acknowledge it was an error
    # muck around with $error here and store it in $_[0]
    # $_[0] is the error message seen by RaiseError/PrintError
    $_[0] = 'The gremlins are loose again!';

    # potentially change the error too
    $dbh->set_err(1234, $_[0]);
  }

  print "\tEnd sub\n\n";

  # return our handled flag
  return $handled;
}

__END__
Trying HandleError (with RaiseError on):
handle it?  no

        Sub 'handle_error': DBD::mysql::db selectall_hashref failed: T
+able 'test
.test' doesn't exist
        End sub

The gremlins are loose again! at ./database.pl line 24.
errstr says: Table 'test.test' doesn't exist [err was 1146 now 1234]
The gremlins are loose again!

----------------------------------------

Trying HandleError (with RaiseError on):
handle it?  yes

        Sub 'handle_error': DBD::mysql::db selectall_hashref failed: T
+able 'test
.test' doesn't exist
        End sub

correct_col     -->     foo
wrong_col       -->     bar
[download]

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