Do not render the reference ID and key columns if RN does not equal.

[chrshnv]

This PR ensures that the ID and key columns of the reference table are not rendered when rn does not match with singlequeryloading enabled.

Closes #2122

[lsh1215]

Hi, thanks for working on this.

I previously commented on #2122 that I wanted to work on the issue, but I wasn’t able to follow up at the time. I recently came back to it and noticed this PR.

While investigating the issue back then, I had also tried a similar change: rendering the reference id/key columns as null when the corresponding row number does not match rn. From what I saw, that addresses the correctness problem where a missing child row can still have non-null id/key columns and therefore be materialized incorrectly.

However, the part I got stuck on was the PostgreSQL performance concern described in #2122. The generated query shape still seems to build the child inline views without restricting them to the selected root ids, so on large tables PostgreSQL can still scan/window over many unrelated child rows before the outer join.

If that sounds reasonable, I’d like to work on the performance part as a follow-up PR, separately from this correctness fix. I’m happy to align with whatever direction the maintainers prefer.