CREATE TABLE customer(c_id int primary key,
    name varchar(20)
    ,address varchar(100),
     city varchar(20),
     ph_no int);

create table product(p_id int primary key,
     pname varchar(20),
     price int default '0');

create table Invoice_master(inv_id int primary key,
     cust_id int ,
     inv_date date,
     constraint fk foreign key(cust_id) references customer(c_id));

create table Invoice_item(invid int,pid int,quantity int,
constraint fkh foreign key(invid) references Invoice_master(inv_id),
constraint frk foreign key(pid) references product(p_id));