Question

我必须确定哪个客户产生了最多的总收入。我设法创建了一个查询，列出了所有客户以及他们产生了多少收入。

SELECT P.FirstName, P.LastName, SUM(BookingFee) AS Revenue
FROM Person P, Customer C, Reservation R
WHERE C.Id = P.Id AND R.AccountNo = C.AccountNo
GROUP BY C.AccountNo
ORDER BY Revenue DESC

通过按降序排列，产生最多收入的客户位于最前面。但我必须让查询只生成一行，其中包含最高收入的客户。我不太清楚如何做到这一点，或者我现在的情况如何正确。

任何收入都与预订表中的BookingFee属性相关联。

这是我的数据库的相关部分和一些示例数据

DROP DATABASE IF EXISTS flight_reservation_system_2;

CREATE DATABASE flight_reservation_system_2;

USE flight_reservation_system_2;



CREATE TABLE Person (
    Id INTEGER,
    FirstName VARCHAR(50) NOT NULL,
    LastName VARCHAR(50) NOT NULL,
    Phone CHAR(10) NOT NULL,
    Address VARCHAR(100) NOT NULL,

    City VARCHAR(50) NOT NULL,
    State VARCHAR(50) NOT NULL,
    ZipCode INTEGER NOT NULL,
    PRIMARY KEY (Id),
    CHECK (Id > 0),
    CHECK (Phone > 0),
    CHECK (ZipCode > 0)
);

CREATE TABLE Employee (
    Id INTEGER NOT NULL,
    SSN INTEGER,
    IsManager BOOLEAN NOT NULL,
    StartDate DATE NOT NULL,
    HourlyRate NUMERIC(10 , 2 ) NOT NULL,
    PRIMARY KEY (SSN),
    FOREIGN KEY (Id)
        REFERENCES Person (Id),
    UNIQUE (Id),
    CHECK (SSN > 0),
    CHECK (HourlyRate > 0)
);

CREATE TABLE Customer (
    Id INTEGER NOT NULL,
    AccountNo INTEGER,
    CreditCardNo CHAR(16),
    Email VARCHAR(50),
    CreationDate DATETIME NOT NULL,
    Rating INTEGER,
    PRIMARY KEY (AccountNo),
    FOREIGN KEY (Id)
        REFERENCES Person (Id),
    CHECK (Rating >= 0 AND Rating <= 10)
);

CREATE TABLE Reservation (
    ResrNo INTEGER,
    ResrDate DATETIME NOT NULL,
    BookingFee NUMERIC(10 , 2 ) NOT NULL,
    TotalFare NUMERIC(10 , 2 ) NOT NULL,
    RepSSN INTEGER,
    AccountNo INTEGER NOT NULL,
    PRIMARY KEY (ResrNo),
    FOREIGN KEY (RepSSN)
        REFERENCES Employee (SSN),
    FOREIGN KEY (AccountNo)
        REFERENCES Customer (AccountNo),
    CHECK (ResrNo > 0),
    CHECK (BookingFee >= 0),
    CHECK (TotalFare > BookingFee)
);


INSERT INTO Person(Id, FirstName, LastName, Phone, Address, City, State, ZipCode)
VALUES(1, 'John', 'Doe','1231231234', '123 N Fake Street', 'New York', 'New York', 10001),
(2, 'Jane', 'Smith','5555555555', '100 Nicolls Rd','Stony Brook', 'New York', 17790),
(3, 'Rick', 'Astley','3141592653', '1337 Internet Lane', 'Los Angeles', 'California', 90001);

INSERT INTO Customer(Id, AccountNo, CreditCardNo, Email, CreationDate, Rating)
VALUES(1, 2, NULL, 'jbdoe@woot.com', '2011-01-01 19:30:00', 8),
(2,  1, NULL, 'awesomejane@ftw.com', '2011-01-01 19:30:00', 5),
(3,3, NULL, 'rickroller@rolld.com', '2011-01-01 19:30:00', 2);

INSERT INTO Reservation(ResrNo, ResrDate, BookingFee, TotalFare, RepSSN, AccountNo)
VALUES(111 , '2010-01-03 19:30:00', 10, 1200.00, NULL, 1),
(222 , '2011-01-03 19:30:00', 30, 500.00,NULL, 2),
(333 , '2011-01-03 19:30:00', 25, 3333.33, NULL, 3);

Answer 1

使用LIMIT：

LIMIT子句可用于约束SELECT语句返回的行数。 LIMIT需要一个或两个数字参数。

SELECT P.FirstName, P.LastName, SUM(BookingFee) AS Revenue
FROM Person P, Customer C, Reservation R
WHERE C.Id = P.Id AND R.AccountNo = C.AccountNo
GROUP BY C.AccountNo
ORDER BY Revenue DESC
LIMIT 1

结果：

FIRSTNAME   LASTNAME    REVENUE
John        Doe         30

请参阅SQL Fiddle中的结果。

确定哪个客户产生了最多的收入

1 个答案: