MySQL 8.0

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create table customer (
    customer_id int not null,
    name varchar (20),
    lastname varchar(20),
    registration_date date,
    primary key (customer_id)
);
create table inventory (
    item_id int not null,
    item_name varchar(20), 
    cost int,
    primary key (item_id)
);
create index some_idx on inventory(item_name);
create table purchase (
    purchase_date date,
    purchase_count int, 
    customer_id int,
    item_name varchar(20),
    foreign key (customer_id) references customer(customer_id),
    foreign key (item_name) references inventory(item_name)
);