Cannot display Row with MySQL and ReactJS

I am new developer ReactJS, I develop a table with ReactJS on the FrontEnd, NodeJS on BackEnd and MySQL about the database. I want to get a data with Select request by Code (Primary key ) on the list.

As you see above, I want, when I click on the view button, it will be directed me to the list page, which the row is retrieved.

My ViewClients :

class ViewClient extends Component {

    constructor(props) {
        super(props);


        this.state = {
            clients: []
        };

        this.toggle = this.toggle.bind(this);
        this.state = {
            activeTab: '1',
        };
    }

    toggle(tab) {
        if (this.state.activeTab !== tab) {
            this.setState({
                activeTab: tab,
            });
        }
    }
    componentDidMount() {
        var Code = this.props.Code;
        axios({
                method: "get",
                url: "/app/viewclient/?Code="+Code+",
                withCredentials: true,
                headers: {
                    "Access-Control-Allow-Origin": "*",
                    "Content-Type": "application/json",
                    Accept: "application/json"
                }
            })
            .then(response => {
                if (response && response.data) {
                    this.setState({ clients: response.data });
                }
            })
            .catch(error => console.log(error));
    }


    render() {
        let { clients } = this.state;
        return (
            <div className="animated fadeIn">
        <Row>
         
           <Col xs="12" md="6" className="mb-4">
            <Nav tabs>
              <NavItem>
                <NavLink
                  className={classnames({ active: this.state.activeTab === '1' })}
                  onClick={() => { this.toggle('1'); }}
                >
                  <i className="fa fa-info"></i> <span className={this.state.activeTab === '1' ? '' : 'd-none'}> Détails</span>
                </NavLink>
              </NavItem>
              <NavItem>
                <NavLink
                  className={classnames({ active: this.state.activeTab === '2' })}
                  onClick={() => { this.toggle('2'); }}
                >
                  <i className="fa fa-credit-card"></i> <span
                  className={this.state.activeTab === '2' ? '' : 'd-none'}> Factures</span>
                </NavLink>
              </NavItem>
              <NavItem>
                <NavLink
                  className={classnames({ active: this.state.activeTab === '3' })}
                  onClick={() => { this.toggle('3'); }}
                >
                  <i className="fa fa-truck"></i> <span className={this.state.activeTab === '3' ? '' : 'd-none'}> Bons de livraison</span>
                </NavLink>
              </NavItem>
            </Nav>
            <TabContent activeTab={this.state.activeTab} style={{ height:"420px"}}>
              <TabPane tabId="1">
               <ul>
               {
                       clients &&  clients.map(client => (
                            <li key={client.Code}>
                         <h1> Code client :    {client.Code} </h1>
                             {client.Prenom}
                              {client.Nom}
                              {client.FAX}
                             {client.Telephone}
                               {client.Email}
                                {client.Adresse1}
                                 {client.Adresse2}
               </li>
               ))}
               </ul>
              </TabPane>
              <TabPane tabId="2">
                
              </TabPane>
              <TabPane tabId="3">
              
              </TabPane>
            </TabContent>
          </Col>
          
        </Row>
      </div>
        );
    }
}

export default ViewClient;

My router is :

    exports.viewclient = function(req, res) {
        var Code = req.params.Code;
console.log(Code);
        connection.query("SELECT Code, Prenom, Nom, FAX, Telephone, Email, Adresse1, Adresse2  FROM clients WHERE Code =?',[Code],  function(error, results, fields) {
            if (error) throw error;
            res.send(JSON.stringify(results));
    console.log(results);
        });
    
    }

My server is :

router.get('/viewclient/:Code?', clients.viewclient);

When I run it, I get on my console backend [] and on my frontend, nothing is showing because the row is not retrieved. How to fix that please ?