protected function buildShowMeta($showMeta, &$params)
    {
        if (empty($showMeta)) {
            return '';
        }
        $sql = 'SHOW META';
        if (is_bool($showMeta)) {
            return $sql;
        }

        if ($showMeta instanceof Expression) {
            foreach ($showMeta->params as $n => $v) {
                $params[$n] = $v;
            }
            $phName = $showMeta->expression;
        } else {
            $phName = self::PARAM_PREFIX . count($params);
            $escape = ['%'=>'\%', '_'=>'\_', '\\'=>'\\\\'];
            $params[$phName] = '%' . strtr($showMeta, $escape) . '%';
        }

        $sql .= " LIKE {$phName}";
        return $sql;
    }