SQL系列房间已售出或可用于一系列日期

Question

关于酒店预订系统还有其他帖子，我有一些好主意。但是，我坚持使用SQL查询。我想要的是出售房间的查询结果。每天需要有一排，每天每种房型都有一个房间出售的数量。例如，它看起来会这样，但是缺少room_types为0：

我已经能够创建一个查询，该查询将生成一系列日期，然后计算每个日期销售的房间。如果没有任何room_type出售房间，则在剩余字段中提供带有NULL的日期行。这是查询：

SELECT the_date::date, bookings.room_type, COUNT(bookings.id) as booked
FROM generate_series('2018-04-04'::date, '2019-04-04'::date, interval '1 day') the_date
LEFT JOIN (SELECT arrival_date, id, departure_date, room_type
        FROM bookings 
        WHERE cancelled IS NULL
        AND checked_out IS NULL)
        bookings
    ON the_date BETWEEN bookings.arrival_date AND (bookings.departure_date - INTERVAL '1 DAY')
GROUP BY the_date, bookings.room_type
ORDER BY the_date, bookings.room_type

我的问题是，即使特定房型没有任何预订，我也需要显示所有房型。它应该在预订列中显示房间类型为0。我有一个room_types表，其中room_type是主键，预订中的room_type采用外键。我尝试加入room_types表但是我的数据不正确。

预订表如下所示：

Room_types表如下所示：

Answer 1

您可以像这样使用CROSS JOIN

SELECT the_date::date, rt.room_type, COUNT(bookings.id) as booked
FROM generate_series('2018-04-04'::date, '2019-04-04'::date, interval '1 day') the_date
CROSS JOIN room_types rt
LEFT JOIN (SELECT arrival_date, id, departure_date, room_type
        FROM bookings 
        WHERE cancelled IS NULL
        AND checked_out IS NULL)
        bookings
    ON the_date BETWEEN bookings.arrival_date AND (bookings.departure_date - INTERVAL '1 DAY') and 
       bookings.room_type = rt.room_type
GROUP BY the_date, rt.room_type
ORDER BY the_date, rt.room_type