final public function fetchColumnDefs(string $table) {
        $tableKey = strtolower($table);

        if (!empty($this->tables[$tableKey]['columns'])) {
            $this->tables[$tableKey]['columns'];
        } elseif ($this->tableNames !== null && !isset($this->tableNames[$tableKey])) {
            return null;
        }

        $columnDefs = $this->fetchColumnDefsDb($table);
        if ($columnDefs !== null) {
            $this->tables[$tableKey]['columns'] = $columnDefs;
        }
        return $columnDefs;
    }