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Re: primary key display in psql

From: "Ross J(dot) Reedstrom" <reedstrm(at)rice(dot)edu>
To: pgsql-hackers(at)postgresql(dot)org
Subject: Re: primary key display in psql
Date: 2010-01-14 17:23:36
Message-ID: 20100114172336.GB27848@rice.edu (view raw or flat)
Thread:
Lists: pgsql-hackers
On Wed, Jan 13, 2010 at 05:03:33PM -0500, Robert Haas wrote:
> On Wed, Jan 13, 2010 at 4:47 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> >
> > Spelling out "primary key" would seem to be more in keeping with existing
> > entries in that column, eg we have "not null" not "NN".
> >
> > I think this is a sensible proposal for a single-column PK, but am less
> > sure that it makes sense for multi-col.  The modifiers column is
> > intended to describe column constraints; which a multi-col PK is not,
> > by definition.
> 
> Yeah, IIRC, MySQL shows PRI for each column of a multi-column primary
> key, and I think it's horribly confusing.  I wouldn't even be in favor
> of doing this just for the single-column case, on the grounds that it
> makes the single and multiple column cases asymmetrical.  IMO, the \d
> output has too many bells and whistles already; the last thing we
> should do is add more.

How about spelling it as so:

     Table "public.test"
  Column |  Type   | Modifiers
 --------+---------+-----------
  a      | integer | primary key
  b      | integer | 
 Indexes:
     "test1_pkey" PRIMARY KEY, btree (a)


     Table "public.test2"
  Column |  Type   | Modifiers
 --------+---------+-----------
  a      | integer | primary key (compound)
  b      | integer | primary key (compound)
 Indexes:
     "test2_pkey" PRIMARY KEY, btree (a, b)

As to Tom's point that a compound primary key is a table level
restriction, by definition, participating in such a key is still a 
restriction on what values that column can take. When introspecting
someone else's schema, with a very wide table, seeing '(compound)' 
is a nice strong hint to go looking for the other members of the PK.

Ross
-- 
Ross Reedstrom, Ph.D.                                 reedstrm(at)rice(dot)edu
Systems Engineer & Admin, Research Scientist        phone: 713-348-6166
The Connexions Project      http://cnx.org            fax: 713-348-3665
Rice University MS-375, Houston, TX 77005
GPG Key fingerprint = F023 82C8 9B0E 2CC6 0D8E  F888 D3AE 810E 88F0 BEDE

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