Thread: Adding a Foreign Key

 Hello everyone,

  I know that a Primary Key can be added to a table before it has been created, doing this...

CREATE UNIQUE INDEX table_pkey ON table (atribute);

  Well I wonder if a Foreign Key can also be added and what syntax does it follow.

  Thankyou in advance.

  Stay Safe & Happy.

   :* TankGirl

On Mon, 3 Sep 2001 tankgirl@worldonline.es wrote:

>  Hello everyone,
>
>   I know that a Primary Key can be added to a table before it has been created, doing this...
>
> CREATE UNIQUE INDEX table_pkey ON table (atribute);
>
>   Well I wonder if a Foreign Key can also be added and what syntax does it follow.

alter table <table> add <table constraint definition>

ie something like:
alter table foo add constraint foo_fk foreign key(col)
 references bar(barcol) on update cascade deferrable
 initially deferred;

tankgirl@worldonline.es writes:

>   Well I wonder if a Foreign Key can also be added and what syntax does it follow.

ALTER TABLE foo ADD CONSTRAINT bar FOREIGN KEY (col) REFERENCES table(col) etc.

--
Peter Eisentraut   peter_e@gmx.net   http://funkturm.homeip.net/~peter

> Hello everyone,
>
>   I know that a Primary Key can be added to a table before it has been
created, doing this...
>
> CREATE UNIQUE INDEX table_pkey ON table (atribute);
>
>   Well I wonder if a Foreign Key can also be added and what syntax does it
follow.
>
>   Thankyou in advance.
>
>   Stay Safe & Happy.
>
>    :* TankGirl

See:

http://www.postgresql.org/idocs/index.php?sql-altertable.html

The part you're interested in says:

To add a foreign key constraint to a table:
ALTER TABLE distributors ADD CONSTRAINT distfk FOREIGN KEY (address)
REFERENCES addresses(address) MATCH FULL

Hope this helps,

-- Joe