Hi Dominique:
Take a look to the "unnest()" function. It transforms an array
into a set of rows. I believe I used it in the past to do
something similar to what you need.
Another option is to use a "values" _expression_ (in a subquery) instead of an array, and build the query dynamically.
Best regards.
On 09/05/2023 11:37, Dominique Devienne
wrote:
On Tue, May 9, 2023 at 11:23 AM David Wheeler <hippysoyboy@xxxxxxxxx> wrote:
> Hi. With an integer identity primary key table,
> we fetch a number of rows with WHERE id = ANY($1),
> with $1 an int[] array. The API using that query must return
> rows in the input int[] array order, and uses a client-side
> mapping to achieve that currently.
>
> Is it possible to maintain $1's order directly in SQL? Efficiently?
We’ve done this before with an “order by array_index(id, input_array)”. I forget the actual function consider that pseudo code
Thanks David. I see how this would work.
It was only used for small arrays but never noticed any performance issues
Hmmm, sounds like this would be quadratic though...
Each call to array_index() will be O(N), so turn the sort into O(N^2) just from the array_index() calls,without even considering the sorting itself (which I assume is O(N log N)).
I wonder whether the int[] can be turned into a pseudo table with a ROWNUM extra generated column thatwould then be (LEFT) JOIN'd to the accessed table, so that the original array index is readily accessible.Would something like this be possible in Postgres' SQL?
I could then skip the sort, return that original index as part of the select,and thus be able to read the other columns directly in the correct client-side re-allocated vector-slot / structure...
