Subject: Re: PoC/WIP: Extended statistics on expressions
To: Justin Pryzby <pryzby@telsasoft.com>
Cc: Dean Rasheed <dean.a.rasheed@gmail.com>, pgsql-hackers@postgresql.org
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From: Tomas Vondra <tomas.vondra@enterprisedb.com>
Message-ID: <04b100f9-201b-0bc8-c613-0f918451b599@enterprisedb.com>
Date: Fri, 22 Jan 2021 14:09:04 +0100
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On 1/22/21 5:01 AM, Justin Pryzby wrote:
> On Fri, Jan 22, 2021 at 04:49:51AM +0100, Tomas Vondra wrote:
>>>> | Statistics objects:
>>>> |     "public"."s2" (ndistinct, dependencies, mcv) ON  FROM t
>>
>> Umm, for me that prints:
> 
>>      "public"."s2" ON ((i + 1)), (((i + 1) + 0)) FROM t
>>
>> which I think is OK. But maybe there's something else to trigger the
>> problem?
> 
> Oh.  It's because I was using /usr/bin/psql and not ./src/bin/psql.
> I think it's considered ok if old client's \d commands don't work on new
> server, but it's not clear to me if it's ok if they misbehave.  It's almost
> better it made an ERROR.
> 

Well, how would the server know to throw an error? We can't quite patch 
the old psql (if we could, we could just tweak the query).

> In any case, why are there so many parentheses ?
> 

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.


regards

-- 
Tomas Vondra
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