SQL Server - Invalid Table - sql

Question

I am fairly new to SQL and I can't understand why I am receiving an error when establishing foreign keys as I receive an error saying that the destination table is invalid.
Below is the SQL code, any advice on how to fix would be brilliant! :)
The error appears regarding tblFilms and tblCinemaScreens.
CREATE TABLE tblCustomer (
CustomerID int,
CustomerSurname NVARCHAR(25),
CustomerForename NVARCHAR(20),
CustomerAge int,
CustomerPhoneNumber NVARCHAR(12),
CustomerEmailAddress NVARCHAR(100),
CONSTRAINT PK_tblCustomer PRIMARY KEY CLUSTERED (CustomerID)
)
GO
CREATE TABLE tblBookings (
BookingID int,
FilmShowings TIME,
PriceOfFilm MONEY,
DateOfBooking DATE,
FilmID int,
CinemaScreenID int,
CustomerID int,
CONSTRAINT PK_tblBookings PRIMARY KEY CLUSTERED (BookingID),
CONSTRAINT FK_FilmID FOREIGN KEY (FilmID) REFERENCES tblFilms(FilmID),
CONSTRAINT FK_CustomerID FOREIGN KEY (CustomerID) REFERENCES tblCustomer(CustomerID)
)
GO
CREATE TABLE tblFilms (
FilmID int,
FilmName VARCHAR(100),
FilmDuration int,
AgeRating VARCHAR(3),
CriticScore int,
FilmDescription NVARCHAR(300),
FilmGenre NVARCHAR(20),
FilmStartScreeningDate DATE,
FlimEndScreeningDate DATE,
CinemaScreenID int,
CONSTRAINT PK_tblFilms PRIMARY KEY CLUSTERED (FilmID),
CONSTRAINT FK_tblFilms FOREIGN KEY (CinemaScreenID) REFERENCES tblCinemaScreens(CinemaScreenID)
)
GO
CREATE TABLE tblCinemaScreens (
CinemaScreenID int,
CinemaScreenType NVARCHAR(10),
NumberOfSeats int,
FilmID int,
CONSTRAINT PK_tblCinemaScreens PRIMARY KEY CLUSTERED (CinemaScreenID),
CONSTRAINT FK_tblCinemaScreens FOREIGN KEY (FilmID) REFERENCES tblFilms(FilmID)
)
GO

Answer 1

Cinema screens table does not need a film id and you need to create the tables BEFORE referencing them with FK's
CREATE TABLE tblCinemaScreens (
CinemaScreenID int,
CinemaScreenType NVARCHAR(10),
NumberOfSeats int,
FilmID int,
CONSTRAINT PK_tblCinemaScreens PRIMARY KEY CLUSTERED (CinemaScreenID)
GO
CREATE TABLE tblFilms (
FilmID int,
FilmName VARCHAR(100),
FilmDuration int,
AgeRating VARCHAR(3),
CriticScore int,
FilmDescription NVARCHAR(300),
FilmGenre NVARCHAR(20),
FilmStartScreeningDate DATE,
FlimEndScreeningDate DATE,
CinemaScreenID int,
CONSTRAINT PK_tblFilms PRIMARY KEY CLUSTERED (FilmID),
CONSTRAINT FK_tblFilms FOREIGN KEY (CinemaScreenID) REFERENCES tblCinemaScreens(CinemaScreenID)
)
GO
CREATE TABLE tblCustomer (
CustomerID int,
CustomerSurname NVARCHAR(25),
CustomerForename NVARCHAR(20),
CustomerAge int,
CustomerPhoneNumber NVARCHAR(12),
CustomerEmailAddress NVARCHAR(100),
CONSTRAINT PK_tblCustomer PRIMARY KEY CLUSTERED (CustomerID)
)
GO
CREATE TABLE tblFilms (
FilmID int,
FilmName VARCHAR(100),
FilmDuration int,
AgeRating VARCHAR(3),
CriticScore int,
FilmDescription NVARCHAR(300),
FilmGenre NVARCHAR(20),
FilmStartScreeningDate DATE,
FlimEndScreeningDate DATE,
CinemaScreenID int,
CONSTRAINT PK_tblFilms PRIMARY KEY CLUSTERED (FilmID),
CONSTRAINT FK_tblFilms FOREIGN KEY (CinemaScreenID) REFERENCES tblCinemaScreens(CinemaScreenID)
)
GO

Answer 2

You are trying to create a foreign key on tables before they are made. Comment out the lines in the create table statements that are giving you an error and create the tables. Once the tables are made create the missing foreign keys you need like this:
alter table tblFilms
add CONSTRAINT FK_tblFilms FOREIGN KEY (CinemaScreenID) REFERENCES tblCinemaScreens(CinemaScreenID)
alter table tblBookings
add CONSTRAINT FK_FilmID FOREIGN KEY (FilmID) REFERENCES tblFilms(FilmID)

Answer 3

The answer is they should have not direct relationships
A film is shown on 0 or more screens
You need a join table
rblFilmCinema
filmID fk to tblFilms
screenID fk to tblCinemaScreens
composite PK on filmID, screenID

Answer 4

I would change up the schema some to give yourself more flexibility. I would assume that a film can be on more than one cinema screen so I would take CinemaScreenID off of tblFilms and remove the foreign key. You can also remove FilmID from tblBookings since you have the CinemaScreenID already which has the FilmID.. Another thing to consider might be having multiple films on the same CinemaScreen which would be another tabled called tblCinemaScreenFilms and you would put that CinemaScreenFilmID on the tblBookings instead
CREATE TABLE tblFilms (
FilmID int,
...
CONSTRAINT PK_tblFilms PRIMARY KEY CLUSTERED (FilmID),
)
GO
CREATE TABLE tblCustomer (
CustomerID int,
...
CONSTRAINT PK_tblCustomer PRIMARY KEY CLUSTERED (CustomerID)
)
GO
CREATE TABLE tblBookings (
BookingID int,
CinemaScreenID int,
CustomerID int,
...
CONSTRAINT PK_tblBookings PRIMARY KEY CLUSTERED (BookingID),
CONSTRAINT FK_CinemaScreenID FOREIGN KEY (CinemaScreenID ) REFERENCES tblCinemaScreens(CinemaScreenID),
CONSTRAINT FK_CustomerID FOREIGN KEY (CustomerID) REFERENCES tblCustomer(CustomerID)
)
GO
CREATE TABLE tblCinemaScreens (
CinemaScreenID int,
FilmID int,
...
CONSTRAINT PK_tblCinemaScreens PRIMARY KEY CLUSTERED (CinemaScreenID),
CONSTRAINT FK_tblCinemaScreens FOREIGN KEY (FilmID) REFERENCES tblFilms(FilmID)
)
GO
Option B (preferred)
CREATE TABLE tblCustomer (
CustomerID int,
...
CONSTRAINT PK_tblCustomer PRIMARY KEY CLUSTERED (CustomerID)
)
GO
CREATE TABLE tblFilms (
FilmID int,
...
CONSTRAINT PK_tblFilms PRIMARY KEY CLUSTERED (FilmID),
)
GO
CREATE TABLE tblCinemaScreens (
CinemaScreenID int,
...
CONSTRAINT PK_tblCinemaScreens PRIMARY KEY CLUSTERED (CinemaScreenID)
)
GO
CREATE TABLE tblCinemaScreenFilms (
CinemaScreenFilmID int,
CinemaScreenID int,
FilmID int
CONSTRAINT PK_tblCinemaScreenFilms PRIMARY KEY CLUSTERED (CinemaScreenFilmID),
CONSTRAINT FK_FilmID FOREIGN KEY (FilmID) REFERENCES tblFilms(FilmID),
CONSTRAINT FK_CinemaScreenID FOREIGN KEY (FilmID) REFERENCES tblCinemaScreens(CinemaScreenID)
)
GO
CREATE TABLE tblBookings (
BookingID int,
CustomerID int,
CinemaScreenFilmID int,
...
CONSTRAINT PK_tblBookings PRIMARY KEY CLUSTERED (BookingID),
CONSTRAINT FK_CustomerID FOREIGN KEY (CustomerID) REFERENCES tblCustomer(CustomerID),
CONSTRAINT FK_CinemaScreenFilmID FOREIGN KEY (CinemaScreenFilmID) REFERENCES tblCinemaScreenFilms(CinemaScreenFilmID)
)
GO

Answer 5

You're creating a table - tblFilms - and adding a foreign key to tblCinemaScreens before the second table has been created.
As a help I usually create all tables and then create any foreign key relationships and other constraints.