create table credit card (

card no number primary key,

limit number,

issue date date,

cust id number,

foreign key (cust id) refernces customer

);



create table customer (

cust id number primary key,

cust name varchar(50)





);



create table usage (

usage id number primary key,

card no number,

amount number,

foreign key (card no) refernces credit card

);



insert into credit card values(3530, 15000, '31-may-2013', 1);

insert into credit card values(5172, 10000, '7-jan-2012', 3);

insert into credit card values(2281, 5000, '26-mar-2011', 2);

insert into credit card values(1795, 5000, '5-dec-2009', 1);



insert into customer values(1, 'ABC');

insert into customer values(2, 'DEF');

insert into customer values(3, 'GH');





* Write a trigger which

	1. auto generates usage id

	2. ensures that total usage of a card does not exceed the limit

	3. gives customer 1% discount in any usage if he/she has multiple cards issued



insert into usage values(NULL, 1795, 3003);

insert into usage values(NULL, 1795, 2002);

insert into usage values(NULL, 3530, 6250);

insert into usage values(NULL, 2281, 4000);

insert into usage values(NULL, 2281, 1500);