or download this
# With placeholders
my $sth_test = $dbh->prepare("select distinct cast($date_col as date)
+from ?;") or die;
...
# Error (on disconnect)
DBI::db=HASH(0x32cec98)->disconnect invalidates 1 active statement han
+dle (either destroy statement handles or call finish on them before d
+isconnecting) at ./refresh_dates.pl line n.