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From: Steve Tucknott (TuSol) <[email protected]>
To: Tom Lane <[email protected]>
Cc: PostGreSQL <[email protected]>
Subject: Re: Advice on foreign key and cascading delete design - postgresql 12.6
Date: Tue, 13 Apr 2021 16:48:48 +0100
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
	<[email protected]>

> Maybe I'm missing something, but aren't you just looking for theON
> DELETE CASCADE option of foreign key constraints?
> 			regards, tom lane

Tom,
Maybe it's me that's missing it.

On my subordinate table I have two 'identification' fields - one
containing a varchar for the table name and the other a value for the
PK for that table. So if I add a 'note' on my notes table for my
suppliers table record 1, I would have an entry on notes with
...'suppliers', 1, 'some note text'...
.
..and on my supplier table a record with PK of 1. So supplier PK 1 has
a note of  'some note text'.

How do I set up the FK on the notes table? All I can see is the option
to link on column names, so I can set up:
...CONSTRAINT notes_c1 FOREIGN KEY (foreignRecNo) REFERENCES supplier
...

BUT that doesn't work as far as I can see, as I may have multiple
foreignrecnos on notes with value 1, each of which is dependent on the
foreigntablename as well - but I cannot see how to specify a literal in
the FK constraint. What I think I need is something like:
...CONSTRAINT notes_c1 FOREIGN KEY (foreigntablename,foreignRecNo)
REFERENCES supplier ('supplier',recno) ...



Does any of that make sense?

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