Primary key is Unique identify the rows in a table. The physical designer will take care of creating Pk inorder to improve performance. and FK gives relationship between two tables. The FK column should present in parent table.
On 12/3/09, Michael Moore <michaeljmo...@gmail.com> wrote: > A Candidate key is a column or group of columns that you think has the > possibility of being a good key for the table. It is a design phase issue, > and not an actual physical implementation. > > A primary key is a column or group of columns that is designated to be the > 'primary key'. It is a physical implementation. You use DDL syntax to 'tell' > the database that this is the primary key. A primary key will always have a > corresponding index which the system will automatically create when you > specify the primary key. > > A Foreign Key column or group of columns that serve as a logical pointer > from one row (record) to another. Most often the rows reside in different > tables. An index for for a Foreign Key is optional, but usually desirable > for performance reasons. A 'foreign key constraint' is a foreign key which > you have told the database about. If you don't tell the database about it, > it's still a foreign key, but it is up to the application code to maintain > the integrity. If you tell the database about it (using DDL syntax) by > creating a 'foreign key constraint' then the database can enforce the > referential integrity. > > Regards, > Mike > > On Thu, Dec 3, 2009 at 5:45 AM, raju <rajuadr...@gmail.com> wrote: > >> please tell me the function of primary key and candidate key and >> foreign key >> >> -- >> You received this message because you are subscribed to the Google >> Groups "Oracle PL/SQL" group. >> To post to this group, send email to Oracle-PLSQL@googlegroups.com >> To unsubscribe from this group, send email to >> oracle-plsql-unsubscr...@googlegroups.com >> For more options, visit this group at >> http://groups.google.com/group/Oracle-PLSQL?hl=en > > -- > You received this message because you are subscribed to the Google > Groups "Oracle PL/SQL" group. > To post to this group, send email to Oracle-PLSQL@googlegroups.com > To unsubscribe from this group, send email to > oracle-plsql-unsubscr...@googlegroups.com > For more options, visit this group at > http://groups.google.com/group/Oracle-PLSQL?hl=en -- You received this message because you are subscribed to the Google Groups "Oracle PL/SQL" group. To post to this group, send email to Oracle-PLSQL@googlegroups.com To unsubscribe from this group, send email to oracle-plsql-unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/Oracle-PLSQL?hl=en
