db design

Hi,

I'm starting my first attempt at creating tables and stuff for my friend.

it started out ok cause I got some help from my other friend but 'm kinda lost now.

I want to use mysql..but I also want to use postgres and make use of other stuff like foreignkeys and stuff

I also want to track which auto parts are compatible with which cars. (1 part can be used on many car models)

i also dunno how keys work..(i haven't defined any primary keys, i dunno which should be and which shouldn't be)
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CREATE TABLE part_categories (
category_id INT(3) NOT NULL AUTO_INCREMENT,
category VARCHAR(30),
);

CREATE TABLE companies (
company VARCHAR(30),
contact_person(20),
address VARCHAR(30),
city VARCHAR(20),
st_prov VARCHAR(10),
postal_code VARCHAR(10),
country VARCHAR(20),
phone_number CHAR(14),
phone_ext CHAR(4),
email VARCHAR(30),
note VARCHAR(512),
keywords VARCHAR (128),
big_logo BLOB,
sm_logo TINYBLOB
);

CREATE TABLE parts (
part_number CHAR(20),
category,
maker,
name VARCHAR(30),
description VARCHAR(1024),
cost INT(5),
price INT(5),
stock INT(3),
note VARCHAR(512),
keywords VARCHAR (128),
big_logo BLOB,
sm_logo TINYBLOB
);

CREATE TABLE vehicle_types (
id INT(3) NOT NULL AUTO_INCREMENT,
maker VARCHAR(15),
model CHAR(10),
class CHAR(10),
year INT (4),
note VARCHAR(256),
);

CREATE TABLE purchase_items (
invoice_number,
part_number,
quantity INT(4),
unit_price INT(5),
note VARCHAR(128)
);

CREATE TABLE parts_vehicle (
part_number,
vehicle_type_id
);

CREATE TABLE purchases (
invoice_number,
purchase_date DATE,
customer_id
);

CREATE TABLE customers (
ID INT NOT NULL AUTO_INCREMENT,
first_name VARCHAR(10),
last_name VARCHAR(10),
initials CHAR(3),
address VARCHAR(30),
city VARCHAR(20),
st_prov VARCHAR(10),
postal_code VARCHAR(10),
country VARCHAR(20),
home_phone_number CHAR(14),
work_phone_number CHAR(14),
mobile_phone_number CHAR(14),
email VARCHAR(30),
note VARCHAR(128)
);

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