RDBMS - Is it possible to have primary key and foreign key in one table if yes so what is the use of foreign

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Is it possible to have primary key and foreign key in one table if yes so what is the use of foreign key?

Total Answers and Comments: 5

Last Update: November 01, 2007 Asked by: vivek srivastava

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November 22, 2006 06:48:03

neha

RE: Is it possible to have primary key and foreign key...

yes u can foreign key is used to cut short the repeated use of primary key data.

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January 09, 2007 01:34:40

vmshenoy

Member Since: October 2005 Contribution: 508

RE: Is it possible to have primary key and foreign key...

yes v can have.

Foreign key is used to make relationship with another table.V can think foreign key as a copy of primary key from another relational table.

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February 22, 2007 21:19:48

manu

RE: Is it possible to have primary key and foreign key...

yes it possible 2 have foriegn key constraint on the same table where there is a primary key.this is can done by adding a constraint to the table using alter table tblname . the refernce column and table being the base table.
thus one table can have both primary key as well as foreign key constraint.

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March 15, 2007 03:59:09

Nikhil_4_Oracle

RE: Is it possible to have primary key and foreign key...

Dear All

Yes its possible.

Alter table reftab add constraint pk_reftab_col1 primary key;

Alter table reftab add constraint fk_reftab_col2 (col2) references reftab (clo1);

it will work....But there is no sence in doing so..u wll just make duplicate data in same table. Also it will increases the data redudancy...

Regards

Nikhil

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November 01, 2007 01:18:07

Shri

RE: Is it possible to have primary key and foreign key...

Dear Vivek
If I understand your question well you mean to say that is there any possibility to have both primary & foreign keys in the same table .
Well the answer is No. The foreign key (by definition) in a table is the key which is the reference of primary key of different table i.e. the foreign key in a table is the primary key of another table. Therefore in order to make use of foreign key concept the tables should be different (one containing primary key while other containing foreign key).
(Please let me know for any issues).

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