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Re: TODO: DROP COLUMN .. CASCADE

From: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Rod Taylor <rbt(at)rbt(dot)ca>,PostgreSQL Development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: TODO: DROP COLUMN .. CASCADE
Date: 2003-03-06 18:01:17
Message-ID: 200303061801.h26I1HJ11513@candle.pha.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Tom Lane wrote:
> Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> > Tom Lane wrote:
> >> Personally I'm not sold on the sensefulness of the TODO item to begin
> >> with.
> 
> > The current code just drops any index that inludes the dropped column,
> > even if the column is the second column in a multi-column index.  Does
> > that seem OK to you?
> 
> What's wrong with it?  Any unique constraint the index might have
> carried is no longer interesting, so there's no semantic reason for
> treating the index as an independent object.  And queries that might
> have referenced the column aren't going to work anymore, so the query
> mix changes and hence the index setup will really need rethinking anyhow.
> 
> Basically I think this proposal would introduce a weird, confusing
> dichotomy of behavior between single- and multi-column indexes.
> And as Rod pointed out, you'd logically have to do the same for CHECK
> constraints depending on whether they mention one or several columns.
> (And what of multicolumn foreign keys?)  I see much confusion ahead,
> and no payback. 

I do see the confusion argument, but I also see cases where folks are
losing the use of an index for single-column lookups.  Others?

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman(at)candle(dot)pha(dot)pa(dot)us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

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