Re: [HACKERS] WITH clause in CREATE STATISTICS

On 21 April 2017 at 01:21, Tomas Vondra <tomas.vondra@2ndquadrant.com> wrote:
> On 04/21/2017 12:13 AM, Tom Lane wrote:
>>
>> Alvaro Herrera <alvherre@2ndquadrant.com> writes:
>>>
>>> Simon just pointed out that having the WITH clause appear in the middle
>>> of the CREATE STATISTICS command looks odd; apparently somebody else
>>> already complained on list about the same.  Other commands put the WITH
>>> clause at the end, so perhaps we should do likewise in the new command.
>>
>>
>>> Here's a patch to implement that.  I verified that if I change
>>> qualified_name to qualified_name_list, bison does not complain about
>>> conflicts, so this new syntax should support extension to multiple
>>> relations without a problem.
>>
>>
>> Yeah, WITH is fully reserved, so as long as the clause looks like
>> WITH ( stuff... ) you're pretty much gonna be able to drop it
>> wherever you want.
>>
>>> Discuss.
>>
>>
>> +1 for WITH at the end; the existing syntax looks weird to me too.
>>
>
> -1 from me
>
> I like the current syntax more, and  WHERE ... WITH seems a bit weird to me.
> But more importantly, one thing Dean probably considered when proposing the
> current syntax was that we may add support for partial statistics, pretty
> much like partial indexes. And we don't allow WITH at the end (after WHERE)
> for indexes:
>
> test=# create index on t (a) where a < 100 with (fillfactor=10);
> ERROR:  syntax error at or near "with"
> LINE 1: create index on t (a) where a < 100 with (fillfactor=10);
>                                             ^
> test=# create index on t (a) with (fillfactor=10) where a < 100;

OK, didn't know about WHERE clause; makes sense.

Currently WITH is supported in two places, which feels definitely
wrong. The WITH clause is used elsewhere to provide optional
parameters, and if there are none present it is optional.

OK, so lets try...

1.
No keyword at all, just list of statistics we store (i.e. just lose the WITH)
CREATE STATISTICS s1 (dependencies, ndistinct) ON (a, b) FROM t1 WHERE
partial-stuff;

and if there are options, use the WITH for the optional parameters like this
CREATE STATISTICS s1 (dependencies, ndistinct) WITH (options) ON (a,
b) FROM t1 WHERE partial-stuff;

2.
USING keyword, no brackets
CREATE STATISTICS s1 USING (dependencies, ndistinct) ON (a, b) FROM t1
WHERE partial-stuff;

and if there are options, use the WITH for the optional parameters like this
CREATE STATISTICS s1 USING (dependencies, ndistinct) WITH (options) ON
(a, b) FROM t1 WHERE partial-stuff;


I think I like (2)

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