字段列表中的列不明确

Question

Table Reservation :

I want to give the guest the amount he has to pay and I have a procedure

CREATE DEFINER=`root`@`localhost` PROCEDURE `CalculateTotal`(IN ID int ,OUT total float)
BEGIN
SELECT (DATEDIFF(reservation.endDate, reservation.startDate) * room.price)
INTO total
FROM (select * from guest Where guestID = ID) As R , Room, Reservation
WHERE Room.roomNumber = Reservation.roomNumber AND Reservation.guestID =
R.guestID;
END

System.out.println("Enter your ID guest:");
int gID = keyboard.nextInt();
rs = stmt.executeQuery("Select guestID from reservation where guestID = "+gID+";");
if(rs.next())
   {
   stmt.executeQuery("call calculateTotal(" + gID + ", @result);");
   rs = stmt.executeQuery("Select firstName, lastName, roomNumber, class, price, startDate, endDate,  @result as TotalPrice From (Guest join (Reservation join Room on (Reservation.roomNumber = Room.roomNumber)) on Reservation.guestID = Guest.guestID ) where reservation.guestID = "+gID+";");
   while(rs.next())
       System.out.println("Name: "+ rs.getString("firstName")+" "+ rs.getString("lastName")+ "  Room Number:"+ rs.getInt("roomNumber") + "  Class:"+ rs.getString("class")+ "  Price:"+ rs.getFloat("price")+ rs.getDate("startDate")+"  EndDate: "+ rs.getDate("endDate")+ "  Total Price: "+ rs.getFloat("TotalPrice") + "р.");
   }

End I have an error

java.sql.SQLIntegrityConstraintViolationException: Column 'roomNumber' in field list is ambiguous
    at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:117)
    at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:97)
    at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:122)
    at com.mysql.cj.jdbc.StatementImpl.executeQuery(StatementImpl.java:1200)
    at com.jdbc.Main.main(Main.java:172)

172 raw is rs = stmt.executeQuery("Select firstName, lastName...

May be somehow improve the procedure and code?

Answer 1

The exception, as @Abra and @Eric Brandt point out, is that you're querying multiple tables, and you would need to prefix the fields with the table names, or aliases, to prevent references to ambiguous columns (eg columns that have the same name in different tables)

Since, you're looking to improve the code, I would make a few suggestions.

As @Strawberry suggests, the procedure is not necessary if the end goal is just to query for a reservation. While it may be possible that you intend to expand the functionality of the procedure, it's generally better IMHO to avoid them for simple calculations, aggregations, etc. that could be done in plain SQL.

Concatenating strings together to form SQL, while using user input, can be dangerous. It's safe in this case, since keyboard.nextInt() would prevent a SQL injection attack, but you might consider using prepared statements to get additional level of protection, and prepared statements can have other advantages as well. For example, some databases will cache the runplan, which can be significant when a more complex query will be run a number of times.

You may always want to user an "on" clause in your joins. Otherwise you will get a cross join, which may not be what you want.

Once you get beyond simple examples, embedding SQL in Java code can become tedious, and externalizing it as a resource can be very useful, and sets up for templating the SQL, or having variations to deal with quirks between different databases (eg MySQL vs Oracle vs Postgres, etc.).

There are a whole bunch of opinions out there about things like natural keys vs surrogate keys, or lowerCamel columns vs lower snake case columns, when to use or avoid stored procedures, etc., but rather than attempt an exhaustive "best practices" list,which would just be my opinion anyway, here's an alternate example that's not too far from your original example (ie ignoring ORM's, etc)

import java.nio.file.Files;
import java.nio.file.Paths;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.Statement;
import java.util.Scanner;

public class Hotel {

    private static Connection connection;
    private static ResultSet rs;
    private static Scanner keyboard;
    private static Statement stmt;

    public static void main(String[] args) throws Exception {
        if (args.length != 3) {
            // Note: Don't pass passwords on the command line in real life.
            System.err.println("Usage: java Hotel <dbUrl> <dbUser> <dbPwd>");
            return;
        }
        // Initial set up
        keyboard = new Scanner(System.in);
        connection = DriverManager.getConnection(args[0], args[1], args[2]);
        stmt = connection.createStatement();
        // Do it the original way (from the post).
        // orig();
        // Do it a slightly different way.
        anotherWay();
    }

    public static void orig() throws Exception {
        System.out.println("(orig) Enter your ID guest:");
        int gID = keyboard.nextInt();
        rs = stmt.executeQuery("Select guestID from Reservation where guestId = " + gID + ";");
        if (rs.next()) {
            stmt.executeQuery("call calculateTotal(" + gID + ", @result);");
            rs = stmt.executeQuery(
                    "Select firstName, lastName, Reservation.roomId as roomNumber, class, price, startDate, endDate,  @result as TotalPrice From (Guest join (Reservation join Room on (Reservation.roomId = Room.id)) on Reservation.guestID = Guest.id ) where Reservation.guestID = "
                            + gID + ";");
            while (rs.next()) 
                System.out.println("  Name: " + rs.getString("firstName") + " " + rs.getString("lastName")
                + "\n  Room Number: " + rs.getInt("roomNumber") + "\n  Class: " + rs.getString("class")
                + "\n  Price: " + String.format("%.2f", rs.getFloat("price")) + "\n  Start Date: "
                + rs.getDate("startDate") + "\n  EndDate: " + rs.getDate("endDate") + "\n  Total Price: "
                + String.format("%.2f", rs.getFloat("TotalPrice")));

        }
    }

    public static void anotherWay() throws Exception {
        System.out.println("(anotherWay) Enter your guest ID:");
        int guestId = keyboard.nextInt();
        // Get the SQL as a String.  Normally this would be standardized into
        // a utility, so it wouldn't be so messy.
        String sql = new String(
                Files.readAllBytes(Paths.get(Hotel.class.getResource("select_reservation.sql").toURI())));
        // Prepare the statement
        PreparedStatement ps = connection.prepareStatement(sql);

        // Set the parameter
        ps.setInt(1, guestId);
        ResultSet rs = ps.executeQuery();
        while (rs.next()) {
            printResult(rs);
        }
        rs.close();
        ps.close();
    }

    public static void printResult(ResultSet rs) throws Exception {
        System.out.println(
                "  Name: " + rs.getString("firstName") + " " + rs.getString("lastName") 
                + "\n  Room Number: "   + rs.getInt("roomNumber") 
                + "\n  Class: " + rs.getString("class") 
                + "\n  Price: " + String.format("%.2f", rs.getFloat("price")) 
                + "\n  Start Date: " + rs.getDate("startDate")
                + "\n  EndDate: " + rs.getDate("endDate") 
                + "\n  Room Charge: " + String.format("%.2f", rs.getFloat("roomCharge"))
                + "\n  Extra: " + String.format("%.2f", rs.getFloat("extra"))
                + "\n  Total Price: " + String.format("%.2f", rs.getFloat("totalPrice"))
                );
    }
}

Run it like this (don't use passwords on the command line in real life)...

java Hotel <url> <user> <pwd>

The output should look like this for guest 1...

(anotherWay) Enter your guest ID:
1
  Name: Alice Smith
  Room Number: 1
  Class: premium
  Price: 100.00
  Start Date: 2020-05-15
  EndDate: 2020-05-22
  Room Charge: 700.00
  Extra: 350.00
  Total Price: 1050.00

and this for guest 2...

(anotherWay) Enter your guest ID:
2
  Name: Bob Jones
  Room Number: 2
  Class: base
  Price: 75.00
  Start Date: 2020-05-15
  EndDate: 2020-05-22
  Room Charge: 525.00
  Extra: 0.00
  Total Price: 525.00 

Here's the externalized SQL...

select
    Guest.firstName,
    Guest.lastName,
    Room.id as roomNumber,
    Room.class,
    Room.price,
    Reservation.startDate,
    Reservation.endDate,
    (DATEDIFF(Reservation.endDate, Reservation.startDate) * Room.price) as roomCharge,
    IFNULL(extra.charges,0) as extra,
    ((DATEDIFF(Reservation.endDate, Reservation.startDate) * Room.price)
        + IFNULL(extra.charges,0)) as totalPrice
from    
    Reservation
    inner join Guest on Reservation.guestId = Guest.id
    inner join Room on Reservation.roomId = Room.id
    left join ( -- Use subquery to calculate extra charges.
        select  -- Could be more efficient by specifying key.
            guestId,
            sum(price) as charges
        from
            RoomService
            inner join Service on RoomService.serviceId = Service.id
        group by
            guestId) extra on extra.guestId = Guest.id
where
    Reservation.guestId = ?;

Here's a full MySQL schema if you want to try it out...

-- Make it idempotent
drop database if exists hotel;
create database hotel;

-- Create the tables (using lowerCamel cols)
CREATE TABLE hotel.Guest (
    id int AUTO_INCREMENT ,
    firstName varchar(40),
    lastName varchar (40),
PRIMARY KEY (id)
);
CREATE TABLE hotel.Room (
    id int AUTO_INCREMENT ,
    class varchar(40),
    price decimal(13,2),
PRIMARY KEY (id)
);
CREATE TABLE hotel.Reservation (
    id int AUTO_INCREMENT ,
    guestId int,
    roomId int,
    startDate date,
    endDate date,
PRIMARY KEY (id)
);

CREATE TABLE hotel.Service (
    id int AUTO_INCREMENT ,
    name varchar(40),
    price decimal(13,2),
PRIMARY KEY (id)
);

CREATE TABLE hotel.RoomService (
    id int AUTO_INCREMENT ,
    guestId int,
    roomId int,
    serviceId int,
PRIMARY KEY (id)
);

INSERT INTO hotel.Guest (id,firstName,lastName) VALUES (1,'Alice','Smith');
INSERT INTO hotel.Guest (id,firstName,lastName) VALUES (2,'Bob','Jones');
INSERT INTO hotel.Guest (id,firstName,lastName) VALUES (3,'Mallory','Adams');

INSERT INTO hotel.Room (id,class,price) VALUES (1,'premium',100.00);
INSERT INTO hotel.Room (id,class,price) VALUES (2,'base',75.00);
INSERT INTO hotel.Room (id,class,price) VALUES (3,'budget',50.00);

INSERT INTO hotel.Reservation (id,guestId,roomId,startDate,endDate) VALUES (1,1,1,'2020-05-15','2020-05-22');
INSERT INTO hotel.Reservation (id,guestId,roomId,startDate,endDate) VALUES (2,2,2,'2020-05-15','2020-05-22');

INSERT INTO hotel.Service (id,name,price) VALUES (1,'WIFI',100.00);
INSERT INTO hotel.Service (id,name,price) VALUES (2,'Safe',100.00);
INSERT INTO hotel.Service (id,name,price) VALUES (3,'Washing clothes',450.00);
INSERT INTO hotel.Service (id,name,price) VALUES (4,'Food delivery',250.00);

INSERT INTO hotel.RoomService (id,guestId,roomId,serviceId) VALUES (1,1,1,1);
INSERT INTO hotel.RoomService (id,guestId,roomId,serviceId) VALUES (2,1,1,4);

DELIMITER //
CREATE DEFINER=`root`@`localhost` PROCEDURE hotel.CalculateTotal(IN ID int ,OUT total float)
BEGIN
    SELECT 
        (DATEDIFF(Reservation.endDate, Reservation.startDate) * Room.price)
    INTO 
        total
    FROM 
        (select * from Guest Where id = ID) As R , 
        Room, 
        Reservation
WHERE 
    Room.id = Reservation.roomId 
    AND Reservation.guestId = R.id;
END //

DELIMITER ;