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Re: [HACKERS] Parser bug?

From: "Oliver Elphick" <olly(at)lfix(dot)co(dot)uk>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: hackers(at)postgreSQL(dot)org
Subject: Re: [HACKERS] Parser bug?
Date: 1998-11-24 17:29:22
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
Tom Lane wrote:
  >"Oliver Elphick" <olly(at)lfix(dot)co(dot)uk> writes:
  >> (Mind you, I think I have not yet got a reliable way of finding the
  >> ultimate ancestor of an inherited constraint.  Is it actually possible to
  >> do this with queries or do we have to add a boolean flag to pg_relcheck
  >> to be set where the constraint is/is not inherited?)
  >In fact, I was about to point out that the query you were describing
  >couldn't possibly give you a reliable answer, quite independent of
  >whether the backend is implementing it properly or not.

Yes, I had been using a concrete example; the results were not
sufficiently general.
[... skip example ...]

  >It seems to me that the correct way to do this is to compare each of a
  >table's constraints against its immediate parent's constraints, and omit
  >from the child any constraints that have the same rcname AND the same
  >rcsrc as a constraint of the parent.  (You need not look at anything
  >other than the immediate parent, because constraints inherited from
  >more distant ancestors will also be listed for the parent.)

That looks good.  I'll see if I can do it that way.

  >There is a case that pg_relcheck does not allow you to distinguish,
  >and that is whether or not the child definition was actually written
  >with a redundant constraint:
[...skip example...]

  >since it cannot tell that childx's constraint wasn't simply inherited.
  >However, it's not clear to me that suppression of redundant constraints
  >is a bad thing ;-)
It seems to be quite reasonable to drop them.

Oliver Elphick                                Oliver(dot)Elphick(at)lfix(dot)co(dot)uk
Isle of Wight                    
               PGP key from public servers; key ID 32B8FAA1
     "Jesus saith unto him, I am the way, the truth, and the
      life; no man cometh unto the Father, but by me."      
                                         John 14:6 

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