Re: [PATCH] Support for Array ELEMENT Foreign Keys

On Mon, Oct 22, 2012 at 2:29 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> I'm not thrilled with the inconsistency either, but given the
> constraints we're under, it seems like the best we can do.  (I feel,
> as Andrew does, that shoving WHERE into the table-constraint syntax
> would not be an improvement; but the column-constraint syntax really
> needs to start with a fully-reserved word).  Have you got a better
> proposal?

Well, I think if that's the best we can do, you original proposal of
ditching the column constraint syntax altogether might be for the
best.  I wasn't too excited about that before, but I think having two
different syntaxes is going to be even worse.  In some ways, it's
actually sort of sensible, because the referring side isn't really the
column itself; it's some value extracted therefrom.  You can imagine
other variants of that as well, such as the recently-suggested

FOREIGN KEY ((somecol).member_name) REFERENCES othertab (doohicky)

Now, what would the column-constraint version of that look like?  Is
it even sensible to think that there SHOULD be a column-constraint
version of that?  I'm not convinced it is sensible, so maybe decreeing
that the table constraint version must be used to handle all
non-trivial cases is more sensible than I initially thought.

-- 
Robert Haas
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