Hi,
On 03/02/2016 05:17 PM, Thom Brown wrote:
...
Well, firstly, the patches all apply.
But I have a question (which is coming really late, but I'll ask it
anyway). Is it intended that CREATE STATISTICS will only be for
multivariate statistics? Or do you think we could add support for
expression statistics in future too?
e.g.
CREATE STATISTICS stats_comment_length ON comments (length(comment));
Hmmm, that's not a use case I had in mind while working on the patch,
but it sounds interesting. I don't see why the syntax would not support
this - I'd like to add support for expressions into the multivariate
patch, but that will still require at least 2 columns to build
multivariate statistics. But perhaps it'd be possible to relax the "at
least 2 columns" requirement, and collect regular statistics somewhere.
So I don't see why the syntax could not work for that case too, but I'm
not going to work on that.
I also note that the docs contain this:
CREATE STATISTICS [ IF NOT EXISTS ] statistics_name ON table_name ( [
{ column_name } ] [, ...])
[ WITH ( statistics_parameter [= value] [, ... ] )
The open square bracket before WITH doesn't get closed. Also, it
indicates that columns are entirely options, so () would be valid, but
that's not the case. Also, a space is missing after the first
ellipsis. So I think this should read:
CREATE STATISTICS [ IF NOT EXISTS ] statistics_name ON table_name (
{ column_name } [, ... ])
[ WITH ( statistics_parameter [= value] [, ... ] ) ]
Yeah, will fix.
regards
--
Tomas Vondra http://www.2ndQuadrant.com
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