From: | Justin Pryzby <pryzby(at)telsasoft(dot)com> |
---|---|
To: | "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com> |
Cc: | Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>, Matthias van de Meent <boekewurm+postgres(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: MERGE and parsing with prepared statements |
Date: | 2022-07-15 20:43:41 |
Message-ID: | 20220715204341.GO18011@telsasoft.com |
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Lists: | pgsql-hackers |
On Fri, Jul 15, 2022 at 12:59:34PM -0700, David G. Johnston wrote:
> On Fri, Jul 15, 2022 at 12:40 PM Justin Pryzby <pryzby(at)telsasoft(dot)com> wrote:
>
> >
> | If the expression for any column is not of the correct data type, automatic type conversion will be attempted.
> > That appears to be copied from the INSERT page.
> > What does that mean, if not that data types will be resolved as needed ?
>
> Yep, and the system needs to resolve the type at a point where there is no
> contextual information and so it chooses text.
I don't know if that's a viable interpretation. The parser "resolved the type"
by assuming a default, which caused an error before finishing parsing.
In the case of INSERT, "conversion will be attempted" means it looks for a cast
from the source type to the target type, and its "automatic type conversion"
will fail if (for example) you try to insert a timestamp into an int.
In the case of MERGE, that same sentence evidently means that it assumes a
default source type (rather than looking for a cast) and then fails if it
doesn't exactly match the target type.
Should that sentence be removed from MERGE ?
--
Justin
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