當(dāng)我使用 memberId 注冊會員時，如何檢查用戶 id 是否已存在于 members 表中？我試過下面的方法。主鍵是 MemberIDMemberDbController.javapublic static boolean checkMemberID(int memberId){        boolean memberIdExists = false;        Connection conn=DBConnection.getDBConnection().getConnection();        Statement stm = conn.createStatement();        ResultSet rst = stm.executeQuery("SELECT * FROM members WHERE memberId='"+memberId+"'");        String id;        if (rst.next()){            id = rst.getString("memberId");            if(id.equals(memberId)){                memberIdExists = true;            }        }        return memberIdExists;    }MemberUiController.java@FXMLvoid addMember(ActionEvent event) {     //Getting Value from User Input     int memberId = Integer.parseInt(memberIdField.getText());      String name = nameField.getText();     String doa = doaField.getText();     RadioButton selectedRadioButton = (RadioButton)      Gender.getSelectedToggle(); //Getting Selected Radio Button     String gender = selectedRadioButton.getText();     String email = emailField.getText();     String phone = phoneField.getText();     try {         if(MemberDbController.checkMemberID(memberId)){             Member member = new Member(memberId,name,doa,gender,email,phone);             int i = MemberDbController.AddMember(member);             if (i > 0) {                                             //Insert Success Alert                                                    }             else{                //Insert Failed Alert             }         }else{             //Member ID Already Exists Alert..!         }    } catch (ClassNotFoundException e) {        e.printStackTrace();    } catch (SQLException e) {        e.printStackTrace();    }}它會針對重復(fù)條目和新條目拋出一個已經(jīng)存在的警報。