Re: Multi-column distinctness.

On 10/20/2015 05:59 PM, Tom Lane wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> On Tue, Oct 20, 2015 at 10:51 AM, Tomas Vondra
>> <tomas(dot)vondra(at)2ndquadrant(dot)com> wrote:
>>>>> ISTM that we could use COLLECT STATISTICS instead of ADD STATISTICS, and
>>>>> use REMOVE STATISTICS instead of DROP STATISTICS. That way we can use
>>>>> ALTER TABLE rather than inventing a new command. 5 minute change...
>
>>> That seems like a neat idea, actually. I'm not sure COLLECT is a good choice
>>> as it suggest the statistics is actually built, but that only happens during
>>> ANALYZE. But otherwise this seems to solve the issues with keywords and it's
>>> quite simple.
>
>> But ADD is no better there. I think ALTER TABLE .. COLLECT STATISTICS
>> isn't any worse than ALTER TABLE ... CLUSTER ON index_name. In both
>> cases, it means, when you do this operation, do it this way.
>
>> I would suggest that instead of DROP or REMOVE, the opposite should be
>> ALTER TABLE .. NO COLLECT STATISTICS.
>
> Why is this an improvement over using already-existing keywords?

The problem is that the actual syntax is ADD [COLUMN], so we can't
simply use ADD STATISTICS as that would mean a conflict in the grammar.
Resolving it means either making COLUMN non-optional, or adding
STATISTICS to reserved keywords - both options break existing code.

regards

--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services