⭐ in reply to What is the difference between $DBI::errstr and $dbh->errstr?
$dbh->errstr is a method call on a database handle. It returns the text of the last error from "the last driver function called," according to the DBI manpage.
In general, you should use $dbh->errstr, unless you don't have an available database handle. For example, if you're calling DBI->connect, you're creating a database handle, so you don't actually have one to call the errstr method on. So if you're doing error checking on the connect method, you should print out $DBI::errstr if you get undefined back from connect.
When you're doing error checking for any database handle methods (prepare, execute, etc.), you should use $dbh->errstr. (Or just set RaiseError.)