You should use the $dbh->table_info(...) method.

It will return a statement handle, that iterates the table(s) you define, thus alloowing easy check whether a table exists.

Your call would be something like

$sth=$dbh->table_info("", $schema, $table_name, "TABLE");
if ($sth->fetch) {
   # table exists
} else {
   # doesn't
}
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This will work on all DBD's (as soon as the authors have implemented the table_info method - most have). If yours doesn't work, then please contact your DBD-author and help him get it done.