Re: WITH clause in CREATE STATISTICS

Moin,

On Thu, April 20, 2017 8:21 pm, Tomas Vondra wrote:
> On 04/21/2017 12:13 AM, Tom Lane wrote:
>> Alvaro Herrera <alvherre(at)2ndquadrant(dot)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;

While I'm not sure about where to put the WITH, so to speak, I do favour
consistency.

So I'm inclinded to keep the syntax like for the "create index".

More importantly however, I'd rather see the syntax on the "ON (column)
FROM relname" to be changed to match the existing examples. (Already wrote
this to Simon, not sure if my email made it to the list)

So instead:

CREATE STATISTICS stats_name ON (columns) FROM relname

I'd rather see:

CREATE STATISTICS stats_name ON table(col);

as this both mirrors CREATE INDEX and foreign keys with REFERENCES. It
could also be extended to both more columns, expressions or other tables
like so:

CREATE STATISTICS stats ON t1(col1, col2 / 2), t2 (a,b);

and even:

CREATE STATISTICS stats ON t1(col1, col2 / 2), t2 (a,b) WITH (options)
WHERE t2.a > 4;

This looks easy to remember, since it compares to:

CREATE INDEX idx_name ON t2(a,b) WITH (options) WHERE t2.a > 4;

Or am I'm missing something?

Regards,

Tels