You always should check for errors, maybe the insertion just doesn't happen for some reason and that's why there is no last_insert_id.

Depending on how you open/manage your DB connection, you might want either to raise an exception on error that you would trap within an eval {}; block, or explicitely check the result/error code.

Have a look into DBD::mysql, maybe it helps a bit.

Depending on the chosen way to deal with errors, your code probably should look like

my $tmp_query="insert into <TableName> values('','');"; 
eval {
  $sth = $dbh->prepare($tmp_query); 
  $sth->execute();
  $sth->finish();
};
if ($@) { # error...
}
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or

  $sth = $dbh->prepare($tmp_query); 
  if (!$sth) {
     die "Error:" . $dbh->errstr . "\n";
  }
  if (!$sth->execute) {
     die "Error:" . $sth->errstr . "\n";
  }
  ...
[download]