Question

So, this is my input, I’m designing a hospital database and I’m creating a table that will hold the relationships between the patients in the ‘patients’ table and the rooms in the ‘room’ table (clever, I know).

here’s the statement is used to declare both tables:

create table patient_room
(
pr_id int NOT NULL PRIMARY KEY auto_increment,
patient_id int NOT NULL,
room_id int NOT NULL,
)ENGINE = InnoDB;

create table patients
(
patient_id int  primary key not null auto_increment,
fname varchar(30),
lname varchar(30),
suffix enum('I','II','III','IV','JR','SR'),
sex enum('M','F','U','T'),
eye_color enum('BK','BR','BL','GY','GR','HZ','MN','DX','UN'),
hair_color enum('BK','BR','BN','RD','WH','SN','BD','UN'),
date_of_birth date not null,
height int unsigned not null,
weight int unsigned not null,
admitted datetime not null
) Engine = InnoDB;

here’s my alter statement

alter table patient_room add foreign key (patient_id) references patient(patient_id) on delete cascade on update cascade;

I get the return:

ERROR 1005 (HY000): Can't create table 'Mthomas.#sql-3dac_5f1' (errno: 150)

I was able to alter the table to create a foreign key using

alter table patient_room add foreign key (room_id) references room(room_id) on delete cascade on update cascade;

without error. I do have have patient_id as a foreign key already on another patient_meds table, and I’m thinking that could be the issue… if so? How do I mitigate it?

Answer 1

your table is called patients and not patient. You need to change

alter table patient_room add foreign key (patient_id) references patient(patient_id) on delete cascade on update cascade;

to

alter table patient_room add foreign key (patient_id) references patients(patient_id) on delete cascade on update cascade;
                                                                        ^