private static void deleteCompetitor(Scanner scan){
		//If there are some competitors in table.
		while (!ds.getAllCompetitor().isEmpty()) {
			//Display all competitor for conveniently picking a name.
			ds.printCompetitors(ds.getAllCompetitor());
			System.out.println("please input the name of competitor whom you want to delete:\n"+ goMainMenu);
			String name = scan.next();
			//If user doesn't want to go back to main menu.
			if (!name.equalsIgnoreCase(mainMenuCmd)) {
				//Checking if it is a valid name.
				if (ds.checkExistingOfCompetitor(name)) {
					//While loop for giving more chances to user ensuring the deleting.
					while (true) {
						System.out.println("Deleting this competitor will also delete him from competition.");
						System.out.println("Are you sure you want to delete this competitor?\n"
										+ " \"y\" for yes, \"n\" for going backward, "
										+ goMainMenu);
						String conf = scan.next();
						//If user doesn't want to go back to main menu.
						if (!conf.equalsIgnoreCase(mainMenuCmd)) {
							//If user input "y".
							if (conf.equalsIgnoreCase("y")) {
								//Delete competitor from competitor table first by name user input.
								ds.deleteCompetitorFromCompetitorTable(name);
								System.out.println("Deleting from competitor table successful.");
								System.out.println();
								//If there are any records in competition table about this student.
								if (ds.checkExistingOfCompetition(name)) {
									//Delete them as well by student name.
									ds.deleteCompetitorFromCompetitionTable(name);
									System.out.println("Deleting from competition table successful.");
									System.out.println();
								}
								else{
									//If there is no record of competition about this student.
									System.out.println("There is no record of this competitor in competition table.");
									System.out.println();
								}
								//Print all competitors again to show user the process worked.
								ds.printCompetitors(ds.getAllCompetitor());
							} else if (conf.equalsIgnoreCase("n")) {
								break;//If user regretted then the program will go backward.
							} else {
								System.out.println("please input valid command.");
							}
						} else {
							return;
						}
					}
				}
				else{
					System.out.println("The name you input does not exist in competitor table, please check it again.");
					System.out.println();
				}
			}
			else{
				return;
			}
		}
		System.out.println("There is no any competitor in yet.");
	}