Retrieving of Specific Age Group - mysql

Question

I want to ask some help on SQL Query on how to retrieve bookings with specific age group. Basically, i want to retrieve bookings where there are customers who are Adults and child, these are determined only by date of birth. Children are treated as 15 years old below and adults are more than 15 years of age. I want to retrieve bookings who have children and adults that does not exceed 20yrs of age. No bookings should be retrieve if there is one customer in the booking that has age of more than 20 yrs old. And bookings should have more than 1 customer. Here's a sample table for your reference -
Booking No 123
Customer 1 - March 1, 2008
Customer 2 - Aug 3, 1998
Booking No 456
Customer 1 - March 2, 1986
Customer 2 - Feb 9, 2007
Customer 3 - Apr 10, 1999
Booking No 789
Customer 1 - Jun 7, 1999
The booking that needs to be retrieved is only Booking No 123. No age is provided in the table and computed only using Date of birth - DateDiff.
BookingID
CustomerID
LName
FName
DOB
ReservationID
BookingID
CompanyID
ArrivalDate
CompanyName
This is the where statement that i've put
(SELECT DATEDIFF(YEAR ,bp.DOB,GETDATE())) <= 20 AND (SELECT DATEDIFF(YEAR ,bp.DOB,GETDATE())) < 15
But still pulling bookings containing customers > 20 yrs old.

Answer 1

This should get you the bookings. The date computation should be based on the RESERVATION Arrival Date, as such if considering older or future reservations, getdate() WOULD alter the computed age at the time of arrival.
I am doing a direct join between the reservation and booking tables grouped by booking and qualifying every occupant's age.
SELECT
R.BookingID
FROM
BookingCustomer BC
JOIN Reservation R
ON BC.BookingID = R.BookingID
group by
R.BookingID
having
SUM( case when DATEDIFF(YEAR , BC.DOB, R.ArrivalDate ) < 16 then 1 else 0 end ) > 0
AND SUM( case when DATEDIFF(YEAR , BC.DOB, R.ArrivalDate ) >= 16
and DATEDIFF(YEAR , BC.DOB, R.ArrivalDate ) < 21 then 1 else 0 end ) > 0
AND SUM( case when DATEDIFF(YEAR , BC.DOB, R.ArrivalDate ) > 20 then 1 else 0 end ) = 0
Now, since a booking is all pointing to a same reservation, you COULD grab all the other fields at the same time
SELECT
R.BookingID,
R.ReservationID,
R.CompanyID,
R.ArrivalDate,
R.CompanyName ... rest of query.
If the query nags about non-aggregate fields, you could just wrap the other fields not part of the group by as MAX() since a booking is always pointing to the same respective reservation and the parent reservation details would not change anyhow.
SELECT
R.BookingID,
MAX( R.ReservationID ) ReservationID,
MAX( R.CompanyID ) CompanyID,
MAX( R.ArrivalDate ) ArrivalDate,
MAX( R.CompanyName ) CompanyName ... rest of query.

Answer 2

Okay, now we can see what's going on (and what's going wrong for you).
Your current query has this:
WHERE (SELECT DATEDIFF(YEAR ,bp.DOB,GETDATE()) <= 20
AND (SELECT DATEDIFF(YEAR ,bp.DOB,GETDATE())) < 15
...this can be translated to:
WHERE (the number of times January 1st is passed) <= 20
AND AT THE SAME TIME (the number of times January 1st is passed) < 15
Besides the fact that ANDs are exclusive - rows have to match both conditions - what's going on is that DATEDIFF counts the number of "boundaries" crossed for the given measure:
Returns the count (signed integer) of the specified datepart boundaries crossed between the specified startdate and enddate.
... and of course the boundary for a year would be January 1st.
First, a digression on range-searching on database. What you do this, WHERE DATEDIFF(YEAR ,bp.DOB,GETDATE() <= 20, you usually cause the database to ignore indices, which are ways to speed up queries; this is because it has to calculate a value (here, the difference in the year), for each row in the table (because otherwise it doesn't know if the calculated value matches).
Instead, it's better to do any "math", whenever possible, on constant values, since the database is going to remember them. The form we should use here will also solve the "selecting older customers" problem too:
WHERE DOB <= DATEADD(year, -21, GETDATE())
(This is equivalent to those "you are 21 if you were born on or before this date in the year XXXX" signs you see in grocery stores)
No that that's out of the way, we need to figure out what we actually need. Restating your conditions above, we're looking for bookings with (all of):
At least one customer 20 years or younger
At least one customer younger than 15 years
No customers more than 20 years old
At least two customers.
Now... Presumably we don't care about multiple (or single) customers that are younger than 20 years old, so long as they're also all more than 15 years old, so we should modify the first condition. Also, quite probably we need to warn if there are only customers in a booking who are 15 years or younger - they don't even have an "almost" adult! And quite probably we need to warn if this person would be all alone, too! So the conditions should be changed to:
At least one customer younger than 15 years
No customers 21 years or older
(please tell me if this restatement was incorrect)
Now that we no our conditions, we can write our statement. We are looking for bookings:
SELECT ReservationID, BookingID, CompanyID, ArrivalDate, CompanyName
FROM Booking
Where there is at least one customer younger than 15 years:
WHERE EXISTS (SELECT 1
FROM BookingCustomer
WHERE BookingCustomer.bookingId = Booking.BookingId
-- birthday after 15 years ago today
AND BookingCustomer.dob > DATEADD(year, -15, GETDATE()))
And there is also no customer 21 years or older:
AND NOT EXISTS (SELECT 1
FROM BookingCustomer
WHERE BookingCustomer.bookingId = Booking.BookingId
-- birthday before or on 21 years ago today
AND BookingCustomer.dob <= DATEADD(year, -21, GETDATE()))
side note: most of the time for booked tours and stuff, they only care about ages at the time the trip is taken, not the booking time, or whatever "today" happens to be when you run this. You probably don't want GETDATE(), but something else, likely ArrivalDate. Since you'd be doing math on a column it would again force a table scan, but keeping the age check - and modifying it a bit to take into account how far ahead a booking can be made - would knock out bookings "earlier" because somebody is definitely old enough (or nobody young enough).

Answer 3

Thanks for the detailed response. I tried the suggested query and it's not returning any booking
WHERE EXISTS (SELECT 1
FROM BookingCustomer
WHERE BookingCustomer.bookingId = Booking.BookingId
-- birthday after 15 years ago today
OR BookingCustomer.dob > DATEADD(year, -15, BOOKING.ARRIVALDATE))
AND NOT EXISTS (SELECT 1
FROM BookingCustomer
WHERE BookingCustomer.bookingId = Booking.BookingId
-- birthday before or on 21 years ago today
AND BookingCustomer.dob <= DATEADD(year, -21, BOOKING.ARRIVALDATE))