I looked at your updated code. I don't see anywhere that you failed to call execute(), but I also don't see where you're getting $dbh from.

Switching to selectall_hashref() is possible and may get rid of the error if you properly remove the other DBI calls that it replaces, but it doesn't solve the fundamental problem which is that you're trying to write DBI code but you haven't taken the time to learn the basics of DBI yet. You should start with this tutorial and then have a look at the DBI docs. Copy-and-paste coding is a dangerous thing to do with DBI.