create simple database for joins

orders.sql

create table customers
(
  id        int auto_increment,
  user_name varchar(255) null,
  constraint customers_id_uindex
  unique (id)
);

alter table customers
  add primary key (id);

create table orders
(
  id      int auto_increment
    primary key,
  user_id int null,
  total   int null,
  constraint user_id
  foreign key (user_id) references customers (id)
    on update cascade
    on delete cascade
);

create table stores
(
  id   int auto_increment
    primary key,
  name varchar(255) null
);

create table products
(
  id       int auto_increment
    primary key,
  name     varchar(255) not null,
  store_id int          null,
  constraint store_id
  foreign key (store_id) references stores (id)
    on update cascade
    on delete cascade
);

create table orders_details
(
  id         int auto_increment
    primary key,
  store_id   int    null,
  product_id int    null,
  qt         int    null,
  total      double null,
  order_id   int    null,
  constraint order_id
  foreign key (order_id) references orders (id)
    on update cascade
    on delete cascade,
  constraint product_id_fk
  foreign key (product_id) references products (id),
  constraint store_id_fk
  foreign key (store_id) references stores (id)
    on update cascade
    on delete cascade
);