Inserting data with foreign keys and avoiding duplication - mysql

Question

I'm very beginner at MySQL and have just started to play around with foreign keys and INNER JOIN operator.
So I've made a few tables like:
CREATE TABLE `models`
(
`id` TINYINT UNSIGNED NOT NULL AUTO_INCREMENT,
`name` VARCHAR (255) NOT NULL,
`price` MEDIUMINT UNSIGNED NOT NULL,
PRIMARY KEY( `id` )
);
CREATE TABLE `vendors`
(
`id` TINYINT UNSIGNED NOT NULL AUTO_INCREMENT,
`name` VARCHAR (255) NOT NULL,
`id_model` TINYINT UNSIGNED NOT NULL,
PRIMARY KEY( `id` ),
FOREIGN KEY (`id_model`) REFERENCES models(`id`)
);
CREATE TABLE `cars`
(
`serial_number` MEDIUMINT UNSIGNED NOT NULL,
`id_vendor` TINYINT UNSIGNED NOT NULL,
FOREIGN KEY (`id_vendor`) REFERENCES vendors(`id`),
PRIMARY KEY( `serial_number` )
);
I know how to get output with that. However, the problem is that I don't know how to insert data properly. All I can do is insert data table by table. But how to do it in one query, and if I am inserting Honda Civic and already have Honda Accord, for example, wouldn't it duplicate Honda vendor in the database?

Answer 1

It seems that the structure of the database is not really coherent. Maybe I don't understand what you are trying to do, but ... anyway, here goes.
Assuming that what you want to do is store a list a of cars in a properly normalized relational database, first thing you want to do is think what is happenning in "real life":
Manufacturers (vendors) make/sell cars
Manufacturers (vendors) make different models of cars
Cars have a model (and a serial number in your case)
Models belong to a vendor (manufacturers)
Considering this, your table structure is:
Vendors
- id
- name
Models
- id
- name
- vendor ( foreign key => vendor.id )
Cars
- id
- serial_number
- model ( foreign key => model.id )
You don't need to have a reference to the vendor in the cars table becoause you have a reference to the model, which in turn has a reference to the vendor.
Whe inserting, you do it one by one, making sure that the foreign key entries already exist.
When you insert a car object, you just need to provide the model id.
When you insert a model object you need to provide a vendor id.
So the Honda Civic/Accord situation does not duplicate Honda. The Tables should be something like this:
Vendor
id, name
1, "Honda"
Model
id, name, vendor
1, "Civic", 1
2, "Accord", 1
Cars
id, serial_no, model
1, "A serial", 2 -> a honda accord
2, "Another serial", 1 -> a honda civic
Hope this helps somewhat.

Answer 2

You do need to check if duplicated record exists yourself.
IF EXISTS (SELECT * FROM vendors WHERE Name = 'Honda')
BEGIN
-- Insert into cars with existing vendor id
END
ELSE
BEGIN
IF EXISTIS (SELECT * FROM models WHERE Name = 'your model name')
BEGIN
-- insert into vendors with existing model id
END
ELSE
BEGIN
-- insert into models
-- insert into vendors
-- insert into cars
END
END
You can create stored procedure for it and pass car, vendor and model as parameters.
Or you can list models first, insert them; then all vendors and all cars. Just a silly answer. Welcome more sophisticated solutions.