Обсуждение: How to select the last value/row?
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
On Thu, Jul 6, 2023 at 8:47 AM Shaozhong SHI <shishaozhong@gmail.com> wrote:
Given,ID543321How to select the last one, to end up with1In 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.
On Thu, 6 Jul 2023 at 16:51, David G. Johnston <david.g.johnston@gmail.com> wrote:
On Thu, Jul 6, 2023 at 8:47 AM Shaozhong SHI <shishaozhong@gmail.com> wrote:Given,ID543321How to select the last one, to end up with1In 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
On Thu, Jul 6, 2023 at 9:02 AM Shaozhong SHI <shishaozhong@gmail.com> wrote:
How aboutID543323The 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.
Shaozhong SHI <shishaozhong@gmail.com> 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