Date: Sun, 21 Jul 2019 09:28:04 +0200
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Subject: Re: How do I alter an existing column and add a foreign key which is
 a Primary key to a table?
To: pgsql-admin@lists.postgresql.org,Karen Goh <karenworld@yahoo.com>
From: Holger Jakobs <holger@jakobs.com>
Message-ID: <5CE41E80-274A-44DA-9553-E2DCA260F751@jakobs.com>
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Am 21=2E Juli 2019 02:58:05 MESZ schrieb Karen Goh <karenworld@yahoo=2Ecom=
>:
>Hi all,
>
>With PG4Admin, I am lost=2E

Since pgadmin4 is just a frontend, you're not "lost with pgadmin4", but ma=
ybe with postgresql=2E

>I realised now that the keys are not created and perhaps that is why
>the join query is not working out=2E

Creating a foreign key doesn't magically create the necessary keys for it=
=2E

>Please let me know what is the correct way to alter a column in a table
>to have foreign key to a tutor_id which is also the primary key of that
>table=2E
>
>So, meaning I need to create a foreign key as well as primary key for
>tutor_id=2E
>
>So far, this is what I have attempted but it is not working=2E
>ALTER TABLE tutor_subject
>  ADD CONSTRAINT tutor_subject_pk=20
>    PRIMARY KEY (tutor_id)
>	ADD CONSTRAINT tutor_subject_fk
>	FOREIGN KEY (tutor_id)

This looks like a 1:1 relationship which is to be avoided=2E

One ALTER TABLE command either adds a primary or a foreign key=2E There is=
 no FK without the keyword REFERENCES=2E

FK relationships help in keeping the data consistent, but they are totally=
 unrelated to/useless for SELECT statements and their JOIN operations=2E Th=
is is a common misconception=2E

Regards,

Holger

--=20
Holger Jakobs, Bergisch Gladbach
+49 178 9759012
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