SQL maximum number of records with a common value - mysql

Question

Please consider the following two tables:
Holidays
HolidayID (PK)
Destination
Length
MaximumNumber
...
Bookings
BookingID (PK)
HolidayID (FK)
Name
...
Customers can book holidays (e.g. go to Hawaii). But, suppose that a given holiday has a maximum number of places. e.g. there are only 75 holidays to Hawaii this year (ignoring other years).
So if some customer wants to book a holiday to Hawaii. I need to count the records in Bookings table, and if that number is greater than 75 I have to tell the customer it's too late.
This I can do using 2 MySQL queries (1 to get MaximumNumber for the holiday, 2 to get the current total from Bookings) and PHP (for example) to compare the count value with the maximum number of Hawaii holidays.
But I want to know if there is a way to do this purely in SQL (MySQL in this case)? i.e. count the number of bookings for Hawaii and compare against Hawaii's MaximumNumber value.
EDIT:
My method:
$query1 = "SELECT MaximumNumber FROM Holidays WHERE HolidayID=$hawaiiID";
$query2 = "SELECT COUNT(BookingID) FROM Bookings WHERE HolidayID=$hawaiiID";
So if the first query gives 75 and the second query gives 75 I can compare these values in PHP. But I wondered if there was a way to do this somehow in SQL alone.

Answer 1

Maybe I am missing something, but why not use a subquery to determine the total bookings for each holidayid:
select *
from holidays h
left join
(
select count(*) TotalBooked, HolidayId
from bookings
group by holidayId
) b
on h.holidayId = b.holidayId
WHERE h.HolidayID=$hawaiiID;
See SQL Fiddle with Demo.
Then you could use a CASE expression to compare the TotalBooked to the MaxNumber similar to this:
select h.destination,
case
when b.totalbooked = h.maxNumber
then 'Not Available'
else 'You can still book' end Availability
from holidays h
left join
(
select count(*) TotalBooked, HolidayId
from bookings
group by holidayId
) b
on h.holidayId = b.holidayId
WHERE h.HolidayID=$hawaiiID;
See SQL Fiddle with Demo.
You will notice that I used a LEFT JOIN which will return all rows from the Holidays table even if there are not matching rows in the Bookings table.

Answer 2

Something like this will work. You can fill in the details:
select case
when
(select count(*)
from Bookings
where holidayID = $hawaiiid)
<= MaximumNumber then 'available' else 'sold out' end status
from holidays
etc

Answer 3

You might try something like this:
select case when b.freq < h.MaximumNumber
then 'Available'
else 'Not Available'
end as MyResult
from Holidays h
left join (
select HolidayID
, count(*) as freq
from Bookings
where HolidayID=$hawaiiID
group by HolidayID
) b
on h.HolidayID=b.HolidayID