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How to select the last value/row? 5+ messages / 3 participants [nested] [flat]
* How to select the last value/row? @ 2023-07-06 15:46 Shaozhong SHI <[email protected]> 0 siblings, 1 reply; 5+ messages in thread From: Shaozhong SHI @ 2023-07-06 15:46 UTC (permalink / raw) To: pgsql-sql <[email protected]> Given, ID 5 4 3 3 2 1 How to select the last one, to end up with 1 In Python, there are ways to handle ordered list. In Postgres, is there something similar? Regards, David ^ permalink raw reply [nested|flat] 5+ messages in thread
* Re: How to select the last value/row? @ 2023-07-06 15:51 David G. Johnston <[email protected]> parent: Shaozhong SHI <[email protected]> 0 siblings, 1 reply; 5+ messages in thread From: David G. Johnston @ 2023-07-06 15:51 UTC (permalink / raw) To: Shaozhong SHI <[email protected]>; +Cc: pgsql-sql <[email protected]> On Thu, Jul 6, 2023 at 8:47 AM Shaozhong SHI <[email protected]> wrote: > Given, > ID > 5 > 4 > 3 > 3 > 2 > 1 > > > How to select the last one, to end up with > > 1 > > In Python, there are ways to handle ordered list. > > In Postgres, is there something similar? > ORDER BY ASC so the "last item" appears first, then "LIMIT 1" David J. ^ permalink raw reply [nested|flat] 5+ messages in thread
* Re: How to select the last value/row? @ 2023-07-06 16:02 Shaozhong SHI <[email protected]> parent: David G. Johnston <[email protected]> 0 siblings, 2 replies; 5+ messages in thread From: Shaozhong SHI @ 2023-07-06 16:02 UTC (permalink / raw) To: David G. Johnston <[email protected]>; +Cc: pgsql-sql <[email protected]> On Thu, 6 Jul 2023 at 16:51, David G. Johnston <[email protected]> wrote: > On Thu, Jul 6, 2023 at 8:47 AM Shaozhong SHI <[email protected]> > wrote: > >> Given, >> ID >> 5 >> 4 >> 3 >> 3 >> 2 >> 1 >> >> >> How to select the last one, to end up with >> >> 1 >> >> In Python, there are ways to handle ordered list. >> >> In Postgres, is there something similar? >> > > ORDER BY ASC so the "last item" appears first, then "LIMIT 1" > > David J. > How about ID 5 4 3 3 2 3 The last is 3. Regards, David ^ permalink raw reply [nested|flat] 5+ messages in thread
* Re: How to select the last value/row? @ 2023-07-06 16:09 David G. Johnston <[email protected]> parent: Shaozhong SHI <[email protected]> 1 sibling, 0 replies; 5+ messages in thread From: David G. Johnston @ 2023-07-06 16:09 UTC (permalink / raw) To: Shaozhong SHI <[email protected]>; +Cc: pgsql-sql <[email protected]> On Thu, Jul 6, 2023 at 9:02 AM Shaozhong SHI <[email protected]> wrote: > > How about > ID > 5 > 4 > 3 > 3 > 2 > 3 > > The last is 3. > > There is no concept of "last" in a query unless you define an order. If you really want whatever row really happens to randomly show up in the last result row the use the "row_number()" window function to give each row a number and then sort and limit on that. David J. ^ permalink raw reply [nested|flat] 5+ messages in thread
* Re: How to select the last value/row? @ 2023-07-06 16:12 Tom Lane <[email protected]> parent: Shaozhong SHI <[email protected]> 1 sibling, 0 replies; 5+ messages in thread From: Tom Lane @ 2023-07-06 16:12 UTC (permalink / raw) To: Shaozhong SHI <[email protected]>; +Cc: David G. Johnston <[email protected]>; pgsql-sql <[email protected]> Shaozhong SHI <[email protected]> writes: > How about > ID > 5 > 4 > 3 > 3 > 2 > 3 > The last is 3. You need to reorient your thinking. In SQL, row sets are unordered sets of values --- this is not a Postgres deficiency, it's a fundamental tenet of the relational data model. If you want some kind of ordering, you have to express that by an ORDER BY clause, which means you need something within the data that corresponds to what you want the ordering to be. Your example above is basically nonsense from the standpoint of SQL. regards, tom lane ^ permalink raw reply [nested|flat] 5+ messages in thread
end of thread, other threads:[~2023-07-06 16:12 UTC | newest] Thread overview: 5+ messages (download: mbox mbox.gz follow: Atom feed) -- links below jump to the message on this page -- 2023-07-06 15:46 How to select the last value/row? Shaozhong SHI <[email protected]> 2023-07-06 15:51 ` David G. Johnston <[email protected]> 2023-07-06 16:02 ` Shaozhong SHI <[email protected]> 2023-07-06 16:09 ` David G. Johnston <[email protected]> 2023-07-06 16:12 ` Tom Lane <[email protected]>
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