Horton

Re: PoC/WIP: Extended statistics on expressions

Tomas Vondra <tomas.vondra@enterprisedb.com>

View thread View on postgr.es
From: Tomas Vondra <tomas.vondra@enterprisedb.com>
To: Justin Pryzby <pryzby@telsasoft.com>
Cc: Dean Rasheed <dean.a.rasheed@gmail.com>, pgsql-hackers@postgresql.org
Date: 2021-08-16T13:19:53Z
Lists: pgsql-hackers 

On 8/16/21 3:31 AM, Justin Pryzby wrote:
> On 1/22/21 5:01 AM, Justin Pryzby wrote:
>>> In any case, why are there so many parentheses ?
> 
> On Fri, Jan 22, 2021 at 02:09:04PM +0100, Tomas Vondra wrote:
>> That's a bug in pg_get_statisticsobj_worker, probably. It shouldn't be
>> adding extra parentheses, on top of what deparse_expression_pretty does.
>> Will fix.
> 
> The extra parens are still here - is it intended ?
> 

Ah, thanks for reminding me! I was looking at this, and the problem is 
that pg_get_statisticsobj_worker only does this:

     prettyFlags = PRETTYFLAG_INDENT;

Changing that to

     prettyFlags = PRETTYFLAG_INDENT | PRETTYFLAG_PAREN;

fixes this (not sure we need the INDENT flag - probably not).

I'm a bit confused, though. My assumption was "PRETTYFLAG_PAREN = true" 
would force the deparsing itself to add the parens, if needed, but in 
reality it works the other way around.

I guess it's more complicated due to deparsing multi-level expressions, 
but unfortunately, there's no comment explaining what it does.

regards

-- 
Tomas Vondra
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

Commits

  1. Disallow extended statistics on system columns

  2. Identify simple column references in extended statistics

  3. Don't print extra parens around expressions in extended stats

  4. Change position of field "transformed" in struct CreateStatsStmt.

  5. Add transformed flag to nodes/*funcs.c for CREATE STATISTICS

  6. Stabilize stats_ext test with other collations

  7. Extended statistics on expressions

  8. Reduce duration of stats_ext regression tests

  9. Allow composite types in catalog bootstrap

  10. Convert Typ from array to list in bootstrap

  11. Disallow CREATE STATISTICS on system catalogs