No unique index found for the referenced field of the primary table - sql

Question

When I run the booking table, it show the message "No unique index found for the referenced field of the primary table".
Create Table Customer
CREATE TABLE CUSTOMER
(
CUSTID INTEGER NOT NULL,
FNAME CHAR(18) NOT NULL,
LNAME CHAR(18) NOT NULL,
STREET CHAR(6) NOT NULL,
CITY CHAR(18) NOT NULL,
PROVINCE CHAR(8) NOT NULL,
COUNTRY CHAR(8) NOT NULL,
POSTCODE CHAR(6) NOT NULL,
GENDER CHAR(6) NOT NULL,
PRIMARY KEY (CUSTID)
);
Create Table Booking
CREATE TABLE BOOKING
(
BKGNO INTEGER NOT NULL,
CUSTID INTEGER NOT NULL,
FNO INTEGER NOT NULL,
STATUSID CHAR(3) NOT NULL,
CLASSID CHAR(4) NOT NULL,
ORIG CHAR(18) NOT NULL,
DEST CHAR(18),
DEPTTIME DATE NOT NULL,
ARRTIME DATE NOT NULL,
BKGCITY CHAR(18) NOT NULL,
PAIDBY CHAR(18) NOT NULL,
FPRICE CURRENCY NOT NULL,
TOTPRICE CURRENCY NOT NULL,
PAIDAMT CURRENCY NOT NULL,
BAL CURRENCY NOT NULL,
BKGDATE DATE NOT NULL,
PRIMARY KEY (BKGNO),
INDEX (ORIG,DEST,DEPTTIME, ARRTIME),
INDEX (CUSTID),
FOREIGN KEY (CUSTID) REFERENCES CUSTOMER,
FOREIGN KEY (FNO) REFERENCES FLIGHT_AVAILABILITY(FNO),
FOREIGN KEY(DEST) REFERENCES FLIGHT_AVAILABILITY(DEST),
FOREIGN KEY(DEPTTIME) REFERENCES FLIGHT_AVAILABILITY(DEPTTIME),
FOREIGN KEY(ARRTIME) REFERENCES FLIGHT_AVAILABILITY(ARRTIME),
FOREIGN KEY(DEST,DEPTTIME,ARRTIME) REFERENCES FLIGHT_AVAILABILITY(DEST, DEPTTIME, ARRTIME),
FOREIGN KEY (ORIG) REFERENCES AIRPORT(AIRPORTCD)
);
Create Table Flight Availability
CREATE TABLE FLIGHT_AVAILABILITY
(
FNO INTEGER NOT NULL,
ORIG CHAR(18) NOT NULL,
DEST CHAR(18),
DEPTTIME DATE NOT NULL,
ARRTIME DATE NOT NULL,
FLENGTH INTEGER NOT NULL,
PRIMARY KEY (FNO,ORIG,DEST,DEPTTIME,ARRTIME)
);
Create TableAirport
CREATE TABLE AIRPORT
(
AIRPORTCD CHAR(18) NOT NULL,
CITYID CHAR(18) NOT NULL,
AIRPORTNM CHAR(18) NOT NULL,
AIRPORTTAX CURRENCY,
PRIMARY KEY (AIRPORTCD)
);

Answer 1

This part causes errors:
FOREIGN KEY (FNO) REFERENCES FLIGHT_AVAILABILITY(FNO),
FOREIGN KEY(DEST) REFERENCES FLIGHT_AVAILABILITY(DEST),
FOREIGN KEY(DEPTTIME) REFERENCES FLIGHT_AVAILABILITY(DEPTTIME),
FOREIGN KEY(ARRTIME) REFERENCES FLIGHT_AVAILABILITY(ARRTIME),
FOREIGN KEY(DEST,DEPTTIME,ARRTIME) REFERENCES FLIGHT_AVAILABILITY(DEST, DEPTTIME, ARRTIME)
A foreign key constraint (also called a referential integrity
constraint) designates a column as the foreign key and establishes a
relationship between that foreign key and a specified primary or
unique key, called the referenced key. A composite foreign key
designates a combination of columns as the foreign key.
So a referenced key should be either unique or primary key.
For example:
FOREIGN KEY (FNO) REFERENCES FLIGHT_AVAILABILITY(FNO)
Referenced key = FNO which is not unique and is not a primary key. Although FNO is part of the composite PRIMARY KEY (FNO,ORIG,DEST,DEPTTIME,ARRTIME), it's not unique (the combination of all the columns of the primary key is unique).
P.S. you really don't need so many columns in your primary key in FLIGHT_AVAILABILITY table. You may create a composite unique index on those columns (if it's really required) and create a NOT NULL constraint on each column. In this case you'll have the same checks as in your current composit primary key. But I don't think you need this.