Bug in Oracle

I had created a small test database with the following tables.

create table BOOK

(

       TITLE     char(50)  not null,
       ISBN      char(15)  not null primary key,
       PUBLISHER char(50)  not null,
       YEAR      char(4)   not null,
       CUR_PRICE number    not null
     );

create table BORROWER


     (

       FNAME   char(10),
       MINIT   char(1),
       LNAME   char(10)   not null,
       SSN     number(9) not null primary key,
       ADDRESS char(50),
       BR_TYPE char(5)   not null              references LIMIT(TYPE)
     );

create table COPY


     (

       ACCESSION  char(15) not null primary key,
       COPY_ISBN  char(15) not null            references BOOK(ISBN),
       COPY_PRICE number   not null
     );


create table COPY_BR


     (

       COPY_AC   char(15)  not null primary key references COPY(ACCESSION),
       BSSN      number(9) not null             references BORROWER(SSN),
       DATE_BR   date      not null
     );

On issuing the following query Oracle failed to give an error. Note that ISBN is an attribute of BOOK which is absent in the inner SELECT.

SELECT FNAME,LNAME, TITLE
   FROM BOOK,BORROWER,COPY,COPY_BR
   WHERE (

          BOOK.ISBN = COPY.COPY_ISBN AND
          BORROWER.SSN = COPY_BR.BSSN AND
          COPY.ACCESSION = COPY_BR.COPY_AC AND
          BORROWER.FNAME != 'Sylvester' AND BORROWER.LNAME != 'McCoy' AND
          BOOK.ISBN       IN (
                              SELECT   ISBN
				      ^^^^^^^^
                                 FROM  BORROWER,COPY_BR
                                 WHERE (
                                        BORROWER.SSN = COPY_BR.BSSN AND
                                        BORROWER.FNAME = 'Sylvester' AND
                                        BORROWER.LNAME = 'McCoy'
                                       )
                             )
         );

Vijay

-- 
===============================================================================
Vijay Raghavan                     | We can sort things out together.
Dept of Comp Sc                    | 
Rensselaer Polytechnic Institute   | Ph:(518)-276-4838