使用 DATEDIFF 无法正确计数的 COUNT 函数

Question

我确信这是一个简单的修复，但无法弄清楚。我有一个 COUNT 函数需要计算出租的总数。单独，该功能工作得很好。我曾尝试使用 DISTINCT，调整 GROUP BY 和 ORDER BY，但无济于事。

当我添加 DATEDIFF 函数来租用 NumberofDays 时，COUNT 函数无法按预期方式工作。我应该用“2”而不是“1”得到一些结果。请注意，我需要按 Rentals.Boat_ID 订购。这是我的代码和表格结果。谢谢

SELECT
    BOATS.Boat_Brand,
    COUNT(RENTALS.Boat_ID) AS NumberofRentals,
    DATEDIFF(Day, RENTALS.Rental_StartDay, RENTALS.Rental_EndDay)+1) as NumberofDaysRented
FROM RENTALS
INNER JOIN BOATS
    ON RENTALS.Boat_ID = BOATS.Boat_ID 
GROUP BY
    BOATS.Boat_Brand,
    RENTALS.Rental_StartDay,
    RENTALS.Rental_EndDay
ORDER BY
    COUNT(RENTALS.Boat_ID) DESC;

Boat_Brand	NumberofRentals	NumberofDaysRented
Blue Martin	1	20
Blue Martin	1	35
Boston	1	52
Cherubini	1	11
Dufour	1	10
Eagle Craft	1	19
Motor Yacht	1	17
Motor Yacht	1	47
Grady-White	1	1
Horizon	1	22
Lemsteraak	1	19
Lund	1	64
Mastercraft	1	19
Mastercraft	1	1
Nauticat	1	10
Tracker	1	18
Tracker	1	1
Viking	1	20
Yamaha	1	20

预期表格/结果：

Boat_Brand	NumberofRentals	NumberofDaysRented
Blue Martin	2	55
Motor Yacht	2	64
Mastercraft	2	20
Tracker	2	19
Boston	1	52
Cherubini	1	11
Dufour	1	10
Eagle Craft	1	19
Grady-White	1	1
Horizon	1	22
Lemsteraak	1	19
Lund	1	64
Nauticat	1	10
Viking	1	20
Yamaha	1	20

Answer 1

似乎您只需要按品牌分组并获得租用天数：

SELECT
    BOATS.Boat_Brand,
    COUNT(RENTALS.Boat_ID) AS NumberofRentals,
    SUM(DATEDIFF(Day,RENTALS.Rental_StartDay,RENTALS.Rental_EndDay) + 1)) as NumberofDaysRented
FROM
    RENTALS
    INNER JOIN BOATS ON RENTALS.Boat_ID = BOATS.Boat_ID
GROUP BY
    BOATS.Boat_Brand
ORDER BY
    COUNT(RENTALS.Boat_ID) DESC;