Doubt with PRIMARY KEY in sql!

Question

Dear friends,
Can you please explain me this scenario's problems
create table a ( eno number);
alter table a add( eno1 number primary key);
alter table a drop primary key;when i describe the table still the column eno1 is showing as NOT NULL. and i cannot modify it as NULL also by sayin
alter table a modify ( eno1 null);is it s a problem with oracle itself or have i understood the concepts wrong.
Regards,
Manoj

Answer 1

bluefrog --
Did you repeat the OP's test case exactly? Here is both yours and the OP's on an 11.2.0.2 system and they behave differently.
SQL> create table a(eno number primary key);
Table created.
SQL> desc a;
Name                                                                                      Null?    Type
ENO                                                                                       NOT NULL NUMBER
SQL> alter table a drop primary key;
Table altered.
SQL> desc a;
Name                                                                                      Null?    Type
ENO                                                                                                NUMBER
SQL> select * from v$version;
BANNER
Oracle Database 11g Enterprise Edition Release 11.2.0.2.0 - 64bit Production
PL/SQL Release 11.2.0.2.0 - Production
CORE    11.2.0.2.0      Production
TNS for Solaris: Version 11.2.0.2.0 - Production
NLSRTL Version 11.2.0.2.0 - Production
5 rows selected.
SQL> drop table a purge;
Table dropped.
SQL> create table a(eno number);
Table created.
SQL> alter table a add( eno1 number primary key);
Table altered.
SQL> desc a;
Name                                                                                      Null?    Type
ENO                                                                                                NUMBER
ENO1                                                                                      NOT NULL NUMBER
SQL> alter table a drop primary key;
Table altered.
SQL> desc a;
Name                                                                                      Null?    Type
ENO                                                                                                NUMBER
ENO1                                                                                      NOT NULL NUMBER
SQL>