>> It was only used for small arrays but never noticed any performance issues > > Hmmm, sounds like this would be quadratic though...
True, but it’s cpu time not io, which tends to be orders of magnitude slower
> I wonder whether the int[] can be turned into a pseudo table with a ROWNUM extra generated column that > would 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?
The unnest function mentioned above has a “with ordinality” option which gives easy access to the array index so a simple join would do the trick
I've actually used this approach (array_index) for hundreds of items without even noticing.
The other approach would be to sort your $1 list, and then just do ORDER BY ID?