Re: primary key display in psql

When you look at a table definition with psql \d, one of the arguably
most important pieces of information -- the primary key -- is hidden
somewhere below under "indexes":

Table "public.test2"
Column | Type | Modifiers
--------+---------+-----------
a | integer | not null
b | integer | not null
Indexes:
"test2_pkey" PRIMARY KEY, btree (a, b)

I think we could easily improve that by having it look something like
this instead:

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

Since there can only be one primary key, this should be unambiguous.

I don't have time to code this up right now, but maybe someone feels
inspired. What do you think?

Peter Eisentraut <peter_e(at)gmx(dot)net> writes:
> I think we could easily improve that by having it look something like
> this instead:

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

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.

regards, tom lane

On Wed, Jan 13, 2010 at 4:47 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Peter Eisentraut <peter_e(at)gmx(dot)net> writes:
>> I think we could easily improve that by having it look something like
>> this instead:
>
>>     Table "public.test2"
>>  Column |  Type   | Modifiers
>> --------+---------+-----------
>>  a      | integer | PK
>>  b      | integer | PK
>> Indexes:
>>     "test2_pkey" PRIMARY KEY, btree (a, b)
>
> 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.

...Robert

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
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