public function getServerVersion()
    {
        if ($this->_serverVersion === null) {
            $this->_serverVersion = $this->db->getSlavePdo()->getAttribute(\PDO::ATTR_SERVER_VERSION);
        }
        return $this->_serverVersion;
    }
public function getServerVersion()
    {
        if ($this->_serverVersion === null) {
            $this->_serverVersion = $this->db->getSlavePdo()->getAttribute(\PDO::ATTR_SERVER_VERSION);
        }
        return $this->_serverVersion;
    }
Returns a server version as a string comparable by [[\version_compare()]].
@return string server version as a string.
@since 2.0.14