How to use SELECT in function to compare fields - sql

Question

There are 3 tables: Event, Booking, and Booking_Day.
The idea is that one can book separate days of the event.
I would like to put a constraint on Booking_Day so that Day has to be within Date_Start and Date_End range of the corresponding Event. I decided to use a function that will do this
create table Event
(
Event_ID int identity
constraint Event_pk
primary key nonclustered,
Date_Start date not null,
Date_End date
)
create table Booking
(
Booking_ID int identity
constraint Booking_pk
primary key nonclustered,
Event_ID int not null
constraint Booking_Event_Event_ID_fk
references Event
)
create table Booking_Day
(
Day date not null,
Booking_ID int not null
constraint Booking_Day_Booking_Booking_ID_fk
references Booking,
constraint Booking_Day_pk
primary key nonclustered (Day, Booking_ID)
)
And the function:
CREATE FUNCTION check_if_in_range (
#Event_id int,
#Day DATE
) RETURNS int
BEGIN
declare #result TABLE (Day DATE,Booking_ID INT,Event_ID INT,Date_start DATE, Data_end DATE)
INSERT into #result
SELECT Booking_Day.Day, Booking.Event_ID, Event.Date_Start, Event.Date_End
FROM ((Booking_Day INNER JOIN Booking on Booking_Day.Booking_ID = B.Booking_ID )
INNER JOIN Event on Event.Event_ID = Booking.Event_ID) WHERE Booking_Day.Day = #Day AND B.Event_ID = #Event_id
return ((#Day >= #result.Date_start) AND (#Day <= #result.Data_end))
END
Because of the primary key constraint on Booking_day table, the above should return only one row.
When trying to add function do database I get “[[S0001][137] Must declare the scalar variable “#result".
How do I deal with it? Is my approach entirely wrong and I don’t need a table within the ​function for this?

Answer 1

I don't understand why you would be using a table variable for this. You cannot just refer to a table unless you specify a FROM clause -- you are confusing table variables and scalar variables.
But why bother with variables at all?
IF (EXISTS (SELECT 1
FROM Booking_Day bd INNER JOIN
Booking b
ON bd.Booking_ID = B.Booking_ID INNER JOIN
Event e
ON e.Event_ID = b.Event_ID
WHERE b.Day = #Day AND
b.Event_ID = #Event_id AND
#Day >= e.Date_Start AND
#Day <= e.Data_end
)
)
BEGIN
return 1
END;
return 0