问题
Having looked at some of the other mysql availability query questions on here has got me so far, but the way mine works is slightly different to the others.
Basically I have a table of dates, and each date is a row. Each row contains fields to say the cost, room type, and how many days your booking has to be to book on that date. So if a Hotel has 1 room type, it will have 365 rows, if it has 5 room types, it will have 1825 rows
bd_id int(10) NO PRI NULL auto_increment
bd_room_type varchar(32)
bd_date date NO
bd_price decimal(8,2)
bd_h_id int(8) NO /* Hotel id */
bd_available tinyint(1) /* number of days you must book to include this date */
I get the from and to dates, and fill in the gap in between so I have all the dates for the booking.
$q1 = "SELECT bd_h_id
FROM booking_dates
WHERE bd_date IN ('2011-02-16','2011-02-17','2011-02-18')
AND bd_available <= '3'
AND bd_room_type = 'single'
AND bd_price > '0'
GROUP BY bd_h_id
HAVING count(*) = '3'";
So if the count is the same as the duration, it means all dependencies have been met and it can show the result in the search.
I am then passing that query as a variable into another query, that extracts the hotel info, checks to see if the sub query is returning anything or not.
$q = "SELECT c_title FROM c_content WHERE c_id IN ($q1) AND IF(($q1) > 0, 1, 0)";
This is fine, however if the sub query returns more than 1 hotel, the main query gives me the error:
Subquery returns more than 1 row
I thought because I used 'IN' that it would be ok. Any suggestions? Also when I go about implementing multiple sub queries, the solution will need to work with that too.
I am aware that the way I am doing the rooms isnt as elegant as it could be, however I am not sure how else to achieve the results I need, as because the bookings will usually be bulk bookings (eg more than one room booked at a time, if one room type isnt available during the dates provided then the whole hotel needs to be removed from the search results).
回答1:
IF(($q1) > 0, 1, 0)
This is the part returning the error.
Also, the way you have it, $q1 is being evaluated twice, which is probably not what you want.
If I understand correctly what you're trying to do, then you should be able to just leave this part out. If $q1 returns no rows, then the IN expression simply won't match anything at all.
Should note as well that IN with subqueries is rather inefficient in MySQL; would run much faster with a join:
SELECT `c_title` FROM `c_content` JOIN ($q1) `a` ON `c_content`.`c_id`=`a`.`bd_h_id`
回答2:
The error message is referring to your IF(($q1) > 0, 1, 0) clause at the end of the query. You can't compare a subquery with > if it returns more than one row.
来源：https://stackoverflow.com/questions/5091491/mysql-query-room-availability