Re: WITH clause in CREATE STATISTICS

Here's a patch implementing this idea. From gram.y's comment, the
support syntax is now:

/*****************************************************************************
*
* QUERY :
! * CREATE STATISTICS stats_name [(stat types)] arguments
!
! * where 'arguments' can be one or more of:
! * { ON (columns)
! * | FROM relations
! * | WITH (options)
! * | WHERE expression }

Note that I removed the USING keyword in the stat types list, and also
made it mandatory that that list appears immediately after the new stats
name. This should make it possible to have USING in the relation list
(the FROM clause), if we allow explicit multiple relations with join
syntax there. The other options can appear in any order.

Also, both WITH and WHERE are accepted by the grammar, but immediately
throw "feature not implemented" error at parse time.

I was on the fence about adding copy/equal/out support for the new
StatisticArgument node; it seems pointless because that node does not
leave gram.y anyway.

Unless there are objections, I'll push this tomorrow.

--
Álvaro Herrera https://www.2ndQuadrant.com/
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