Re: Inaccurate description of UNION/CASE/etc type selection
| От | David G. Johnston |
|---|---|
| Тема | Re: Inaccurate description of UNION/CASE/etc type selection |
| Дата | |
| Msg-id | CAKFQuwYjvVgyw5Ehw8JnPPZ1Tjox_yxktdkw5U8gm8nSM=ejJQ@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: Inaccurate description of UNION/CASE/etc type selection (Tom Lane <tgl@sss.pgh.pa.us>) |
| Ответы |
Re: Inaccurate description of UNION/CASE/etc type selection
|
| Список | pgsql-docs |
On Mon, Aug 17, 2020 at 8:31 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
"David G. Johnston" <david.g.johnston@gmail.com> writes:
> More concisely:
> Make the first input type a candidate type. Each subsequent input type is
> compared to the current candidate, with a new candidate being chosen only
> when there exists a non-mutal implicit cast to the new type. If at any
> point a preferred type is made a candidate then it will be chosen.
So this is just a verbatim statement of the algorithm, which is what
I was hoping to avoid :-(. But maybe there's no simpler way.
I got nothin'. The locking onto the preferred type is conditional on one being chosen and there doesn't seem to be any greater principle that emerges from the pairwise matching algorithm - at least given that implicit casts are essentially randomly distributed and the algorithm is order-dependent.
David J.
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