Re: BUG #18467: postgres_fdw (deparser) ignores LimitOption

From: Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>
To: Japin Li <japinli(at)hotmail(dot)com>
Cc: Etsuro Fujita <etsuro(dot)fujita(at)gmail(dot)com>, onderkalaci(at)gmail(dot)com, pgsql-bugs(at)lists(dot)postgresql(dot)org
Subject: Re: BUG #18467: postgres_fdw (deparser) ignores LimitOption
Date: 2024-05-16 16:47:21
Message-ID: 202405161647.dj7lw4asvfpu@alvherre.pgsql
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On 2024-May-17, Japin Li wrote:

> After some dig in, I find transformLimitClause() has the following comments:
>
> * Note: as of Postgres 8.2, LIMIT expressions are expected to yield int8,
> * rather than int4 as before.
>
> So the deparseConst() append '::bigint' typecast, same as get_rule_expr().

Hmm, probably the answer is not to use deparseExpr in
appendLimitClause() then. I mean, AFAICS this is a postgres_fdw
problem, not a core parser problem.

Not sure if this is workable, but maybe test if the value is a constant,
and use FETCH FIRST if so, otherwise fall back to using LIMIT. (It's
not clear if this would handle FETCH FIRST +123123123123 ROWS WITH TIES
correctly though -- worth checking).

Oh, I see we never got back to adding FETCH FIRST / PERCENT. We had a
patch seemingly almost ready for that ...

--
Álvaro Herrera 48°01'N 7°57'E — https://www.EnterpriseDB.com/

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