The definition of a PK constraint is that it is a UK constraint plus the "not null" constraint. Indexing is a technical implementation issue and is not really part of the PK definition. After all Oracle can from verion 8 up use non-unique indexes to implement PK constraints. -----Original Message----- From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx]On Behalf Of dba1 mcc Sent: Tuesday, January 18, 2005 1:59 PM To: oracle-l@xxxxxxxxxxxxx Subject: [Q] what difference between PK and unique index + not NULL?? I have some argued with contractor about Primary key and Unique index + Not NULL. Contractor said Primary Key = (field specify NOT NLL and create unique index ..). I rember some documents say Primary Key and (unique index, not null) still some different. Does anyone have opinion? Thanks. __________________________________ Do you Yahoo!? Yahoo! Mail - Easier than ever with enhanced search. Learn more. http://info.mail.yahoo.com/mail_250 -- //www.freelists.org/webpage/oracle-l -- //www.freelists.org/webpage/oracle-l