Combining two queries in mySQL

问题

I'm trying to combine the results of two queries. I'm not very proficient in mysql so I'm here for some help.

The first query is as follows:

select count(roomtypeid) as bookedrooms, day 
from event_guest_hotel 
where hotelid = 1 and roomtypeid = 1 
 group by day;

This returns:

The second query:

SELECT ehr.reservationid, ehr.day, h.name AS hotelname, 
ehr.totalrooms as requested_rooms, r.name AS roomname
            FROM event_hotel_reservation ehr 
            INNER JOIN hotel_room_type r 
            ON ehr.roomtypeid = r.roomtypeid 
            INNER JOIN hotel h
            ON ehr.hotelid = h.hotelid  
            WHERE totalRooms != 0 
            AND reservationID = '1'

This returns:

Can I combine the first query with the second one, so I get the results of the first one in another resultcolumn next to 'roomname'? That way I know how many rooms are already booked and how many were originally requested from one single query.

回答1:

Try:

SELECT ehr.reservationid, ehr.day, h.name AS hotelname, 
    ehr.totalrooms as requested_rooms, r.name AS roomname, 
    egh.bookedrooms
FROM event_hotel_reservation ehr 
INNER JOIN hotel_room_type r ON ehr.roomtypeid = r.roomtypeid 
INNER JOIN hotel h ON ehr.hotelid = h.hotelid    
left outer join (
    select hotelid, count(roomtypeid) as bookedrooms, day 
    from event_guest_hotel 
    where roomtypeid = 1 
    group by hotelid, day
) egh on h.hotelid = egh.hotelid and ehr.day = egh.day
WHERE totalRooms != 0 
    AND reservationID = '1'

来源：https://stackoverflow.com/questions/7272260/combining-two-queries-in-mysql