Example 1 :

createtable cust
(custno varchar2(5) primarykey,    
 cname varchar2(20) unique,
 state varchar2(10),
 phone number(10),
constraint  st check(statein ('Gujarat','Rajasthan','MP','UP','Maharastra')));


Example 2 :

createtable item
(itemno varchar2(5) primarykey,
 itemname varchar2(20) notnull,
 itemprice number(8,2),
 Qty_hand number(3),
constraint itp check(itemprice>0));


Example 3 :

createtable invoice
(invno number(4) primarykey,
 invdate date,
 custno varchar2(5) references cust);


Example 4 :

createtable invitem
(invno varchar2(5) references invoice,
 Itemno varchar2(5) references item,
 qty number(3),);