| From: | Vik Fearing <vik(at)postgresfriends(dot)org> |
|---|---|
| To: | Tatsuo Ishii <ishii(at)postgresql(dot)org>, david(dot)g(dot)johnston(at)gmail(dot)com |
| Cc: | jacob(dot)champion(at)enterprisedb(dot)com, pgsql-hackers(at)postgresql(dot)org, er(at)xs4all(dot)nl, peter(at)eisentraut(dot)org |
| Subject: | Re: Row pattern recognition |
| Date: | 2024-10-22 13:12:43 |
| Message-ID: | a13e5b7d-c131-44b3-9d2a-2c57d22a8251@postgresfriends.org |
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| Lists: | pgsql-hackers |
On 22/10/2024 12:19, Tatsuo Ishii wrote:
> Acording to ISO/IEC 9075-2:2016 "4.21.2 Row pattern navigation operations",
>
> <row pattern navigation operation> evaluates a <value expression> VE
> in a row NR, which may be different than current row CR.
>
> From this I think PREV(col + 1) should be interpreted as:
>
> 1. go to the previous row.
> 2. evaluate "col + 1" at the current row (that was previous row).
> 3. return the result.
>
> If my understanding is correct, prev(price + 1) has the same meaning
> as prev(price) + 1.
This is how I read the specification also.
--
Vik Fearing
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