Question

I am having trouble setting multiple foreign keys in my house-letting database.

A house has many rooms, which has many tenancies, each with a tenant. A tenant can have many tenancies.

My database is created as follows:

DROP TABLE IF EXISTS house;
CREATE TABLE house
(
    house_name varchar(30) NOT NULL PRIMARY KEY,
    address_first_line varchar(60),
    address_city varchar(30),
    address_postcode varchar(8)
);

-- rooms

DROP TABLE IF EXISTS room;
CREATE TABLE room
(
    house_name varchar(30) NOT NULL,
    room_number smallint NOT NULL,
    PRIMARY KEY(house_name,room_number),
    FOREIGN KEY (house_name) REFERENCES house(house_name)
);

-- tenants

DROP TABLE IF EXISTS tenant;
CREATE TABLE tenant
(
    tenant_id smallint NOT NULL,
    tenant_firstname varchar(20),
    tenant_surname varchar(20),
    tenant_telephone varchar(12)
);

-- rentals

DROP TABLE IF EXISTS tenancy;
CREATE TABLE tenancy 
(
    house_name varchar(30) NOT NULL,
    room_number smallint NOT NULL,
    start_date date NOT NULL,
    end_date date,
    tenant_id smallint NOT NULL,
    advance smallint,
    deposit smallint,
    PRIMARY KEY (house_name,room_number,start_date),
    FOREIGN KEY (house_name,room_number) REFERENCES room(house_name,room_number),
    FOREIGN KEY (tenant_id) REFERENCES tenant(tenant_id)
);

This line is generating a “1005 error: Can’t create table tenancy (errno: 150)”:

FOREIGN KEY (tenant_id) REFERENCES tenant(tenant_id)

The tenancy table is a relationship between tenant and room, which is why it references both tables.

I suspect it is something really simple, but I’m struggling to get it and would appreciate a little help.

Thanks,

Richard

Answer 1

The tenants.tenant_id must be PRIMARY KEY in order to REFERENCE it as FOREIGN KEY.

-- tenants

DROP TABLE IF EXISTS tenant;
CREATE TABLE tenant
(
    tenant_id smallint NOT NULL,
    tenant_firstname varchar(20),
    tenant_surname varchar(20),
    tenant_telephone varchar(12),
    PRIMARY KEY(tenant_id)
);