Re: Why can't I have a "language sql" anonymous block? - Mailing list pgsql-general

From David G. Johnston
Subject Re: Why can't I have a "language sql" anonymous block?
Date
Msg-id CAKFQuwaFyVbaY+SyyuDPR6gBgBivJPAf9_tPRwyUDun-tj7gJg@mail.gmail.com
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In response to Re: Why can't I have a "language sql" anonymous block?  (Adrian Klaver <adrian.klaver@aklaver.com>)
Responses Re: Why can't I have a "language sql" anonymous block?  (Bryn Llewellyn <bryn@yugabyte.com>)
List pgsql-general
On Wed, Dec 15, 2021 at 2:37 PM Adrian Klaver <adrian.klaver@aklaver.com> wrote:
On 12/15/21 13:05, Bryn Llewellyn wrote:
>> mmoncure@gmail.com <mailto:mmoncure@gmail.com> wrote:

> — — — — — — — — — — — — — — — — — — — — — — — — — — — — — —
> About your point #1…
>
> I used a procedure to test this because functions shouldn’t do DDL. I
> started with a working “language plpgsql” example:

Since procedures are relatively new to Postgres you are going to find
more functions doing DDL then procedures. Not sure I follow why one is
preferred over the other anyway?

Unless you are doing transaction control our implementation doesn't really give a preference.  But from a theory perspective functions are ideally side-effect free while procedures are not.  DDL, and even DML, cause side-effects and so are better done within a procedure.  Having side-effects in a SELECT query is likewise not desirable so the inability to actually execute a procedure in the middle of a SELECT command doesn't pose a conceptual problem.

As for the main question of allowing anonymous procedures to be written in SQL, I too don't see much benefit.  The pl/pgsql implementation is basically a superset, aside from adding BEGIN/END; you can simply pretend you are writing plain SQL in the DO body and it should work.  Now, would we reject a well-written patch that made it work?  Probably not.  But given the fact that DO is not a standard proscribed feature, and pl/pgsql works, I see little motivation for anyone to simply complete the symmetry.  If anything, the fact that these procedures would mostly be used for "side-effect causing actions" means that added overhead of the language tends to 0% of the overall execution time as the procedures become more complex and thus benefit more from being wrapped.

David J.

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